I have GE membership and do use GE kiosks from time to time. But I sometimes use APC, sometimes use MPC and sometimes use the same lines as those US visa users not able to use APC. From having used it all a lot, APC kiosks don’t work as MPC, and MPC app doesn’t work for APC kiosk use and MPC app doesn’t work for GE kiosk use.

Is there any ability to use MPC without use of the MPC app versions released by this app’s maker/provider?

Doesn’t seem so to me yet.