diff --git a/src/nix/eval-composition.nix b/src/nix/eval-composition.nix
index c6cf620..56e2538 100644
--- a/src/nix/eval-composition.nix
+++ b/src/nix/eval-composition.nix
@@ -1,4 +1,4 @@
-{ modules ? [], uid ? 0, pkgs }:
+{ modules ? [], uid ? "0", pkgs, hostNixStorePrefix ? "", }:
 
 let _pkgs = pkgs;
 in
@@ -18,14 +18,16 @@ let
 
   builtinModules = [
     argsModule
-    ./docker-compose-module.nix
+    ./modules/composition/docker-compose.nix
+    ./modules/composition/host-environment.nix
   ];
 
   argsModule = {
     _file = ./eval-composition.nix;
     key = ./eval-composition.nix;
     config._module.args.pkgs = lib.mkIf (pkgs != null) (lib.mkForce pkgs);
-    config._module.args.uid = uid;
+    config.host.nixStorePrefix = hostNixStorePrefix;
+    config.host.uid = lib.toInt uid;
   };
 
 in
diff --git a/src/nix/docker-compose-module.nix b/src/nix/modules/composition/docker-compose.nix
similarity index 84%
rename from src/nix/docker-compose-module.nix
rename to src/nix/modules/composition/docker-compose.nix
index 159ff26..63aeace 100644
--- a/src/nix/docker-compose-module.nix
+++ b/src/nix/modules/composition/docker-compose.nix
@@ -9,7 +9,7 @@
     - docker-compose.services
 
  */
-{ pkgs, uid, lib, config, ... }:
+{ pkgs, lib, config, ... }:
 
 let
   evalService = name: modules:
@@ -21,15 +21,16 @@ let
 
       builtinModules = [
         argsModule
-        ./service.nix
-        ./service-host-store.nix
+        ../service/docker-compose-service.nix
+        ../service/host-store.nix
+        ../service/host.nix
       ];
 
       argsModule = {
-        _file = ./docker-compose-module.nix;
-        key = ./docker-compose-module.nix;
+        _file = ./docker-compose.nix;
+        key = ./docker-compose.nix;
         config._module.args.pkgs = lib.mkForce pkgs;
-        config._module.args.uid = uid;
+        config.host = config.host;
       };
 
     in
diff --git a/src/nix/modules/composition/host-environment.nix b/src/nix/modules/composition/host-environment.nix
new file mode 100644
index 0000000..16bf23e
--- /dev/null
+++ b/src/nix/modules/composition/host-environment.nix
@@ -0,0 +1,32 @@
+{ lib, ... }:
+
+{
+  options = {
+
+    host.uid = lib.mkOption {
+      type = lib.types.int;
+      description = ''
+        The numeric user id (UID) of the user running arion.
+
+        Assuming this user id is helpful when dealing with the user's
+        files, mounted into the container as a volume.
+      '';
+    };
+
+    host.nixStorePrefix = lib.mkOption {
+      type = lib.types.string;
+      default = "";
+      example = "/mnt/foo";
+      description = ''
+        Prefixes store paths on the host, allowing the Nix store to be
+        stored at an alternate location without altering the format of
+        store paths.
+
+        For example: instead of mounting the host's /nix/store as the
+        container's /nix/store, this will mount /mnt/foo/nix/store
+        as the container's /nix/store.
+      '';
+    };
+
+  };
+}
diff --git a/src/nix/service.nix b/src/nix/modules/service/docker-compose-service.nix
similarity index 100%
rename from src/nix/service.nix
rename to src/nix/modules/service/docker-compose-service.nix
diff --git a/src/nix/service-host-store.nix b/src/nix/modules/service/host-store.nix
similarity index 66%
rename from src/nix/service-host-store.nix
rename to src/nix/modules/service/host-store.nix
index e650d78..ae6a1e5 100644
--- a/src/nix/service-host-store.nix
+++ b/src/nix/modules/service/host-store.nix
@@ -5,6 +5,7 @@
 
  */
 { lib, config, pkgs, ... }:
+
 let
   inherit (lib) mkOption types mkIf;
 in
@@ -18,10 +19,10 @@ in
   };
   config = mkIf config.service.useHostStore {
     service.image = "arion-base";
-    service.build.context = "${../arion-image}";
+    service.build.context = "${../../../arion-image}";
     service.volumes = [
-      "/nix/store:/nix/store"
-      "${pkgs.buildEnv { name = "container-system-env"; paths = [ pkgs.bashInteractive pkgs.coreutils ]; }}:/run/system"
+      "${config.host.nixStorePrefix}/nix/store:/nix/store"
+      "${config.host.nixStorePrefix}${pkgs.buildEnv { name = "container-system-env"; paths = [ pkgs.bashInteractive pkgs.coreutils ]; }}:/run/system"
     ];
   };
 }
diff --git a/src/nix/modules/service/host.nix b/src/nix/modules/service/host.nix
new file mode 100644
index 0000000..3ba2ee8
--- /dev/null
+++ b/src/nix/modules/service/host.nix
@@ -0,0 +1,11 @@
+{ lib, ... }:
+{
+  options = {
+    host = lib.mkOption {
+      type = lib.types.attrs;
+      description = ''
+        The composition-level host option values.
+      '';
+    };
+  };
+}