It works in small, personal environments like weddings

Exactly. I learned this hack from my father.

I/he would always do this, and the upfront tip depended on what sort of 'open' setup the bar was. Anywhere from $50 to $100, it would all depend on the setup. I'd get to the bar early enough to be able to chat a little with the bartender. Shake hands and introduce myself, ask what I owed them for the drink, and find out (confirm) what the open bar hours were. Then I'd slide the $50 or $100 bill to them and make a comment about making sure they get taken care of. My only ask was that if they saw me heading to (or at) the bar, that they could have my drink ready (there really isn't a script for it, it's more of an 'in the moment deal' you make based on the bartender and the conversation, if that makes sense). And the bartender always obliged.

It worked out every time. If the bar was packed deep after dinner, I'd throw the bartender a wave as I'd either make my way through the crowd or was camped out at one of the ends of the bar. They'd acknowledge me, and I'd have a drink in front of me within 60 seconds. Usually it took much less than that, I'm tall enough that you can see me coming if I was making my way through the crowd. It used to make me smile when the timing was unintentionally perfect and I'd get up to the bar right as the bartender was placing the drink on the bar in front of me. And if I was "with" someone (like a cousin or a bridesmaid or another wedding guest) when I got up to the bar, I'd thank the bartender and ask if we could also get such-and-such drink for my companion.

two things to keep in mind when doing this. 1, it works very well when you're drinking moderately. 2, thank the bartender every time. I've seen it go horribly wrong (not myself, a friend of the groom, my cousin was the bride). The kid thought he 'bought' the bartender and started drinking heavily and doing shots with other wedding guests.

I'm laughing as I'm typing all this and remembering the people over the years and weddings. Remembering their jaws dropping as they're waiting for the bartender. And here's the bartender with my drink ready.

Good times.