Actually, with Cichlids, 'overcrowding' will generally lower aggression.
If there are a bunch of them in there, they will spend their time chasing each other around but they won't ever target and kill one. Think of it as something of a target rich environment that keeps any individual fish from getting pestered to death.
If you can get a good cichild setup and overfilter it a bit, creating a heavily rocked environment with a bunch of fish will be the most healthy and, IMO, attractive solution.
If you can't draw a crowd, draw dicks on the wall.
2013 Adopt-A-Chief: AJ Jenkins, WR #13