Hmm, I didn't know about this one, it looks very nice indeed

Speaking of nice emulators, JavaCPC (
https://sourceforge.net/projects/javacpc/) is also very nice & comes packed with apps.
Since there's no ini file or command line argument that I know of, I don't think I can have a clean integration in GBCPC, but it would be extremely easy to add the emulator & have it launch every time you launch a game (just add the emulator in the GEMUS & point to the exe file). Gamebase automatically uses the first emulator in the GEMU list. But you would have to manually insert the disk & launch it.
The advantage of using what's already implemented is that you just click on "Play Game" (or press ALT+P) & there you go, no fiddling with the emulator. Of course, you need to be aware of how to use the emulator, but that's the joy of emulation

At least CPCE is fairly simple to use (I only use F7 to change disk, F6 to fast forward & ALT+F3 to change tape - the rest is nice but not vital).