Dorm neighbors sounds good to me! That way they could know each other a little better than just in passing, too, even if Ben's a bit on the quiet side, :)
In my head, Blaine transferred just after the Sadie Hawkins dance at his old school, so people who were at Dalton at the time are bound to know why he transferred with visible injuries. It's up to you whether Blaine would know that Ben is gay, too, though -- if Ben's as quiet as he sounds, it's feasible that it's not common knowledge? Just depends on how you'd rather play it, :)