Not to be a party pooper, but this is NOT a good idea. Yeah, the single pipe is ugly, but lets look at the reasons not to do this:
If you cut just unbolt the thing off the headers, it will be so unbelieveably loud that you'll crap yourself. It'll destroy your performance because of the lack of backpressure, and it will utterly decimate your fuel economy because you'll run open-loop all the time. Bad, bad, bad BAD idea.
If you just cut the y-pipe after the cats, you'll still lose some performance (not as much), but at least you'd be able to go closed loop. I'd be careful abour driving in any kind of rain or dusty road, though, pretty good way to have **** flying into your cats and permanently **** them up.
You could just 'nip the tip' off right after the muffler. Wouldn't really make any difference whatsoever, and you wouldn't see the tip anymore...
Further, if you cut it anywhere under the car, you
WILL be breathing fumes. Especially if you cut it closer to the front. I'm not saying it'll kill you, but it sure as hell won't be good for you. If you don't think those fumes will make it into the cabin, you're dead wrong. There's a reason exhaust pipes are at the BACK of the car.
So basically you're talking about turning your car into a hideously loud (and not GOOD loud, BAD loud) monster that pukes fuel all over the place and performs like crap, and huffing on some gas fumes for a few months, all so you don't have to see a little 2" pipe?
I really just think this is a very bad idea. ESPECIALLY when you're getting a new exhaust in a month or two. Just wait. Patience is a virtue. If you REALLY hate that tip that much, just clip it off a few inches back from the bumper. But I wouldn't even bother going that far.