There have been a ton of Guster songs done in college a cappella. You just don't hear many of them out here in SoCal (mostly in the northeast and midwest). Plus, most of the ones I've heard or seen are from Guster's first three albums: Parachute, Goldfly, and Lost and Gone Forever, all which were released in the 90s (back when I was in college), which seems oh so long ago these days. And most of those covers were performed or recorded in the late 90s and early 2000s. Not so many anymore, but that could be because Guster's two most recent albums were not nearly as good as the first three; but that topic is for a much different post on a different forum. :-)
Additionally, wasn't NYU Mass Transit's version of "Mona Lisa" on one of the BOCA albums?