The Guitar Center near my home has models that they'll open and let you test out. They don't have a very good selection, though... last time I went (about a year or two ago), they only had DT770s and HD280 Pros worth mentioning (and some various crappy AKGs that I absolutely did not like; I seem to recall the K240M as one of them).
I haven't dropped by in a while, though... I'll probably do that during winter break with my source and rock out.