i like the idea of the pleco being missed.
if i where you, id give that a try, although this is just because i like plecos so much...
i space permits, get a decent sized one that will not grow too big, but can protect itself from an O's curiosity.
My oscars don't bother my plecos, and the other way around goes the same.
My o's may inspect the pleco's and what they are doing from a couple of milimeters from the plecos head and nose,(REAL close, that is...) and the pleco is used to that and doesn't respond at all!