A gc and wii homebrew application send gameboy roms to a gba with the link cable.

All you need is a folder called "roms" on your main device (sd gecko on gamecube and sd/usb on wii) and put in some gb and gbc files.
If you then start GoombaSend you can just select the file you want and transfer it to your gba in port 2 by pressing a.
This project uses Goomba v2.30 as the gameboy emulator so if you leave your gba inactive for 5 minutes it will automatically go into sleep mode which you can wake up from by pressing start+select.

Please note that because this all gets put into the gba ram the max file size including the goomba gba (42.4kb) is 256kb.
Also you obviously wont be able to save whatsoever since this is all just temporary.