Option to use mp3gain on each file after conversion to mp3

Just to make sure I don't forget to use mp3gain on the m4a's and such that I haven't converted yet, I'd like an option right in the GUI and the CLI (possibly --mp3gain) to mp3gain the file after it's converted to an mp3. I don't know how many mp3gain arguments would be relevant. Maybe provide a choice between -r and -a (Track gain vs. Album gain).