This is a job I will do very rarely, so I would prefer to avoid buying a specialty tool, if possible.
Unfortunately I don't own a dremel. Side cutters just mashed everything and did not cut at all. Are there any other methods you can recommend?
EDIT: I think this is different from the brake cable housing question, in that side cutters will get the job done with a little effort on brake cable. They have a much harder time cutting the parallel strands of derailleur cable housing.
EDIT2: I asked the guys at the store where I bought the housing to cut it to length for me and they didn't mind. :)