This has been on my front-end wishlist forever, but as far as I know has not materialized on any customizable front end.

There are workarounds to do that with Mala and Hyperspin.
See the "multiple emus in one list" sticky in the Mala subforum.
If you're looking for "nice and easy to configure", turn back now.
It's not easy to wrap your head around to begin with, but once you have a complete understanding of how everything in Mala works it becomes easy to add more games.
Basically you point Mala toward a batch file instead of mame.exe and the batch file runs the appropriate emulator based on what sub-folder the rom was found in.
Mala pulls all the info from mame.xml, so you need to add the games to that.
mame.xml has changed recently and Mala is no longer being developed and hasn't been updated to work with the changes, so that adds yet another wrinkle.