I think thats a myth about uaru needing to be kept in groups. Certainly while they're younger its better to have them in a group, but I've found they'll often pair up (even two of the same sex some times) and break away from the group. I've kept them alone and in pairs before with out any problems. A friend actually had to seperate his two at around 6-7" as they didn't get along, they're now quite happy by themselves.
Keep an eye out for a large one for sale by itself, rather than growing one out.
What about heckelii's? They get to around 30cm, look great, and AFAIK aren't super-aggressive like most CA cichlids.