diff --git a/Justfile b/Justfile
index f3ff469..5b66483 100755
--- a/Justfile
+++ b/Justfile
@@ -1,3 +1,6 @@
+_DEFAULT_VERSION_TMPL:
+	echo "{{invocation_directory()}}/nix/variables/versions.tmpl.nix"
+
 _usage:
 	just -l
 
@@ -21,10 +24,10 @@ _rebuild-device dir rebuildarg="dry-activate" +moreargs="": _render_templates
 	set -ex
 	just -v _device rebuild {{dir}} --argstr rebuildarg {{rebuildarg}} {{moreargs}}
 
-rebuild-remote-device dir target rebuildarg="dry-activate" :
+rebuild-remote-device device target rebuildarg="dry-activate" :
 	#!/usr/bin/env bash
 	set -ex
-	just -v _rebuild-device {{dir}} {{rebuildarg}} --argstr moreargs "'--target-host\ {{target}}'"
+	just -v _rebuild-device nix/os/devices/{{device}} {{rebuildarg}} --argstr moreargs "'--target-host\ {{target}}'"
 
 # Rebuild this device's NixOS
 rebuild-this-device rebuildarg="dry-activate":
@@ -66,9 +69,34 @@ rebuild-this-device rebuildarg="dry-activate":
 		fi
 	fi
 
-# This could be used to inject another channel
-# --argstr moreargs "\'-I nixos-unstable=https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz\'"
+update-remote-device device target rebuildmode='switch':
+	#!/usr/bin/env bash
+	set -e
 
+	template=nix/os/devices/{{device}}/versions.tmpl.nix
+	outfile=nix/os/devices/{{device}}/versions.nix
+	
+	if ! test -e ${template}; then
+		template="$(just _DEFAULT_VERSION_TMPL)"
+	fi
+
+	esh -o ${outfile} ${template}
+	if ! test "$(git diff ${outfile})"; then
+		echo Already on latest versions
+		exit 0
+	fi
+
+	just -v rebuild-remote-device {{device}} {{target}} dry-activate || {
+		echo ERROR: rebuild in mode 'dry-active' failed after updating ${outfile}
+		exit 1
+	}
+
+	just -v rebuild-remote-device {{ device }} {{ target }} {{ rebuildmode }} || {
+		echo ERROR: rebuild in mode '{{ rebuildmode }}' failed after updating ${outfile}
+		exit 1
+	}
+
+	git commit -v ${outfile} -m "nix/os/devices/{{ device }}: bump versions"
 
 # Update the channel versions and (by default) switch to new environment
 update-this-device rebuild-mode='switch':
diff --git a/nix/variables/versions.tmpl.nix b/nix/variables/versions.tmpl.nix
new file mode 100644
index 0000000..93b44b8
--- /dev/null
+++ b/nix/variables/versions.tmpl.nix
@@ -0,0 +1,15 @@
+{
+  channelsNixosStable = {
+    ref = "nixos-19.03";
+    rev = "<% git ls-remote https://github.com/nixos/nixpkgs-channels nixos-19.03 | awk '{ print $1 }' | tr -d '\n' -%>";
+  };
+  channelsNixosUnstable = {
+    ref = "nixos-unstable";
+    rev = "<% git ls-remote https://github.com/nixos/nixpkgs-channels nixos-unstable | awk '{ print $1 }' | tr -d '\n' -%>";
+  };
+  homeManagerModule = {
+    url = "https://github.com/rycee/home-manager";
+    ref = "master";
+    rev = "<% git ls-remote https://github.com/rycee/home-manager.git master | awk '{ print $1 }' | tr -d '\n' -%>";
+  };
+}