Thanks for your kind words!!
The forthcoming mGalaxy version will add this option: you'll be allowed to specify a rom folder and get the whole file list regardless their file extension (users will have to be sure that this folder is "clean", so that a .jpeg file isn't send to mame, for instance)
In the meanwhile I would recommend you to check for a "file renamer" on Google.
Those application allow you to batch rename files and files extension.
Renaming a "pacman.7z" to "pacman.zip" won't affect the file itself..and I'm pretty sure that it would be a good solution for you.
Please check and tell me if it works for you!