Improve Butterfly without actually swimming it.

Before I get started, I just want to say that I'm already aware of how nothing can be better than simply swimming the stroke. Anyways, I swim at my city's community center pool and it is quite crowded in the lap lanes, on top of that, the people are not exactly polite. I need to work on my butterfly(and other strokes too, but mostly fly) for when my school's swim season starts, so it's pretty important. Does anyone know any good drills or weight sets that I can possibly do to improve my butterfly without much time in the water? (I'm kinda starting to get sick of playing frogger every day trying to avoid people) Thanks! Oh, on a side note, whenever I swim for a while, I get really noticeable dark circles under my eyes, does anyone know the cause?