TL;DR version:
1.) Thank you for the scalpel suggestion. Between it, tweezers and rubber cement, I made some decent money.
2.) What to do about people that hang around for multiple performances on busy nights?
I raked in my second biggest hat last night using the above routine.

I performed it four times with Svengali/Trilby work in between while trying to build the crowds. I passed the hat too soon after the first. My thinking was in order to get heat off of the cup I'd immediately go to a quick joke and get the hat moving. All that got me were looks of, "Hey, that was amazing! How in t... why the hell are you giving me this hat?"
It was my first time performing with a TT while surrounded. I was so worried about the heat being on the slush cup at the end that I didn't give the TT a second thought about being spotted. I had an unexpected "pop" sound after one of the removals. I haven't had that happen, even in practice, in a while and unfortunately I reacted to it with facial expressions before I caught myself doing it. There was a pause for laughter moment in my patter that generated chuckles which I believe covered the sound but I am still disappointed for reacting the way that I did.
Despite being worried about it, I never had problems with heat on the slush cup or anything else for that matter. Looking back on it now, it was very much a case of, "Stop running, you're not being chased.". I think that the imaginary perimeter that I set up while pulling in crowds also helped to keep them at bay. I also lucked out big time: no drunks and no hecklers.
I had a problem last night (that didn't end up being a problem, I'll explain why in a sec...) that I have only had a couple of times before- groups of 5-10 people hanging out for multiple performances. I don't like it because I worry that one may catch on, or at least think that they did, to a certain move or whatever and start ribbing me. I've never had that happen yet. What I have had happen is them tipping at the first hat but passing on the rest and taking spots of potential punters. Last night was the exception as they threw in a couple of bucks each time.
So... for those that busk, how do you handle loiterers?