1. Ranking up all the classes you are interested in at the same time helps a little in my case. I don't have to hold a lot of armor to be decently optimal.
2. Using general purpose (i.e. for all crafters, for all mages) gear also trades a little performance for space.
3. Use up all the +1/+2/+3 materials first chance you get.

That said, I am also having inventory issues haha...