creating trainers

I've been looking into creating my own trainers for snes/psx/ps2/DC games for a while, but i always get stuck in how to make the the initial gui stuff. as far as permenatly patching roms/isos with hex codes that's easy (but usually to mixed results when actually playing the game). I'd like to start makeing my own trainers for consoles. mainly psx and DC. I want to create a menu with my bg music, (everyone elses sucks), or allow users to set their own. but being able to toggle on / off codes that are conviently place on the disc instead of in a cheat device is hella kick ass. but how do I write a script to tell the trainer to inject the hex code into memory? and compile the trainer to boot first instead of the game? most games have just enough room to fit a small front end like this.

I've been messing around with cools herders and PAR nothing solid yet but maybe soon.