-Use your chosen means to copy the apk(s) to /system/app (this will require making /system/app writable. In Root Manager just press the R/W key when you're exploring /system/app).
-Click on the apk once it's in /system/app and install it.
-Now, you've installed the program, but the system won't see it as a system app unless you change it's permissions. In Root Manager, long press on the app (in /system/app) and click on "permissions". Then make sure that only the following boxes are clicked: User Read, User Write, Group Read, Others Read.
-Make sure you make /system/app read only again by clicking that box in the top right while you're exploring the folder.