i agree with richard (polypterus) on this. bad idea with the situation as is, don't get another big fish for an already cramped tank until you get the bigger tank. TSN's come around all the time, so it's best for everyone (including headaches for you should the longnose break it's back or dealing with ridiculous bioload) if you just hold off until the bigger tank. good luck--
--solomon
PS-- agree on the shortnose issue too...i've kept my fair share of them and none of them have acted like the one in question...great for the owner/fish, but should not be extrapolated to represent the species in general--
--solomon
PS-- agree on the shortnose issue too...i've kept my fair share of them and none of them have acted like the one in question...great for the owner/fish, but should not be extrapolated to represent the species in general--