Best Way to Grease a Hotel Front Desk Worker?

I've been reading with interest in various threads how people have managed to get a room upgrade in Vegas by slipping the front desk worker a twenty or whatever. How the hell do you do this? I want to try, but I'm mortified at the thought of the front desk worker blinking back at me and saying something like, "Sir, this is *not* a Hollywood movie. We do not do that kind of thing around here."

For context, I'm the guy who loves the discount but is mortifyingly embarrassed to ask for it, to negotiate at the car dealer, or to actually present the coupon to the supermarket cashier. Can someone with my pathetic profile successfully grease a front desk worker?

Have you successfully secured a better room (or table or whatever else) with a little grease? How do *you* do it? Like, what are the actual things you do and say?

How much do you slide them?
How do you slide it to them?
What words do you say or signals do you give?
Have you ever been rejected? If so, what happened? How did you handle it?

Gonna be at the WSOP for eight days in June and want to see if I can pull this off. Please share your tips and any helpful/fun stories.

Thanks!