Thanks very much for this.
I’d really like to try it, but all my Megadrive roms are .gen.

Do you think this is a .bin?
http://www.openthefile.net/extension/gen/2908
http://yoyofr.proboards.com/thread/731

For me the emulationstation config looks for these extensions

<extension>.smd .SMD .bin .BIN .gen .GEN .md .MD .zip .ZIP</extension>