I mentioned this in the FI Catback thread - that perhaps the best option would be to cut part of the can and make a flat spot that is parallel to the ground.
Whip out the big disk grinder, grind off the lowest portion maybe .5" up then weld over a flat stainless steel piece that will fit the hole.
Then again, I don't know what the inside structure of the cans are, but, as an idea, it's flawless!
Or, worst cast, sell the FI catback and get something else.