Pretty much what he said. You will have a very hard time adding any other fish. With the addition of the Flame, you are already pushing the limits anyway.
Edit: forgot to add - you could use this as an excuse to upgrade! "well, I was happy with the 40, but since you got me this beautiful fish, and really, it would be happier in a larger tank (choose wisely), I guess I'll just have to get a new tank"
Win Win!!!