I have the same request. I have a lot of sixties pop and it would be nice to have the possibility to add multiple songwriters to a single track.
I add my albums after digitize them to flac with dbpoweramp. The artist and composer id3 tags can contain multiple names separated by a ';'. The artists are all picked up by the scanner in OrangeCD, but the composers are limited to the first name. Maybe it could be a quick solotion to allow the scanner to pick up all names in the composer field.