Well, you can make a custom MAME list like they do for Custom Folders in MAME32, but you'll have to add your games manually to that list. Then if you point it at the folders properly, GameEx will create a custom category for the folders you made. Other than that, no. If you do decide to do that, then you just create a txt file with your games in it and put it in the Custom Lists folder you have GameEx pointed at. It's kinda difficult, but it can be done - specifically if you know the rom name of the file you want to use. Downside is that this is only for MAME, it doesn't work for other emulators.