I was thinking, maybe if you put the jetpack cheat in while you are flying, maybe you appear with it and float in it rather than fall. That way you could fly around before the loading screen flashes up, which as you know, meant that you'd flown too low in the original interior universe. That way you could fly around and see if Liberty City and the hidden tattoo parlour etc are still in the right places. If:
1. They are, then I've found a second way into the interior universe
2. They are not, then I've found a whole different interior universe!
This is obviously based on the idea that the jetpack idea will work. I'm off to test it now!