What about one of those Chinese algae eaters?
I know they're small (roughly 3 inches) but, it would be easier for them to hide, and they're much cheaper than plecos are, so if you lose one, oh well!!
Ghost shrimp are an excellent clean up crew, and they only cost about 15-30 cents, if you buy a bunch, he's got a crunchy snack AND a cleanup crew.
Right now with my P, I have a 4 inch Pleco, 1 crawfish, and 1 snail. The pleco's been in there about as long as the Piranha has. I took Whiplash OUT in order to add the pleco, I also did a bit of rearranging of the tank decor to break up territories, just like I was adding more ps.