On the positive side, wbaw was correct that once the code is triggered, it should use the correct Gen1/Gen2 TPT files from the image folder. I made an image.bin with cpg's ztepack and put it in the image folder then used ZTE's Storage Card Updates option in GSF. The phone rebooted and applied the TPT properly (as far as I can tell, not had any problems yet). I was also able to start the TPT directly from the app without the need for the image.bin file by calling SDRise directly. Only tested this on GSF so far, but it should work on other ZTE stock roms (the Bulgarian stock rom I downloaded for testing a few weeks back has the same code for SDRise as GSF). I looked at the code for SDRise on the CAE and Crevitus roms, and its totally different from GSF. It may turn out to work anyway, but I'll try when I get home.
Other roms are going to be more difficult. All the ones mentioned above have some kind of option for it built into the settings menu already, and they have the Tgetmem file in /system/bin. To get it working in this form on other roms will probably at least need to put Tgetmem in place if I can convert the code to work from the app. If not, it may also mean modifying the settings.apk (if thats even possible from the phone). I think I know how to get Tgetmem into place, but again it still needs testing.
I have a few more ideas I'm going to try, so I'll update with progress/failure later on.