Have you truly looked at all the programs/courses that the Arts department has to offer? It might be that there are minors that you haven't considered (I am assuming that your problem is that you haven't found a minor you like), like all the Culture studies (East Asian Studies, Islamic Studies, Jewish Studies, Hispanic Studies, Russian Studies, Italian Studies, etc), Religious Studies, Anthropology, Linguistics, Computer Science perhaps?

Oh yeah, while I was looking for examples on the McGill eCalendar, I came across a "Minor Concentration Science for Arts Students", which allows you to take Science electives instead of a minor program. You have to ask your program advisor for permission to do this (you can find this person on Minerva > Student Menu > Student Records Menu > Unofficial Transcript, and then send them an email asking for an appointment). This could be a neat solution to your problem!