This tidbit might help, courtesy of GirLuvsDroid:
The easiest way to make an update.zip file for loading an app in /system/app (the "cheater's method") is as follows:
-On your PC, take one of the theme files compatible with the ROM you're using, right click on it and open it as an archive using 7zip or WinRar (don't ever unzip this file!)
-Inside the zip archive, you'll see 2 folders: META-INF and system
-Don't touch the META-INF folder
-Open the system folder and delete the framework folder
-Open the app folder and delete all the apps in there, then drag the stock .apk you're getting into that app folder
-Close the zip archive and rename it something descriptive.