There's no "force update"
If you have whatever LG uses for desktop software, you should hypothetically be able to download it from there without waiting for the OTA. Based on Software version & updates: LG G3 it may not exist.
As for rollouts, I THINK it's generally <5% the first week, 25% the second week, then 75-100% the third week? It's all some random algorithm nobody's ever been privy to.
Yeah the T mobile rep didn't seem like pushing the update would work, but said they would give it a try. The updates probably going to take longer now since some people are having issues, but thats alright. Thanks