Using Vacation to Stall

The simple solution is to only play in events that don't allow vacation. You can also petition the site to make no vacation random seeks as well, though that has been a request for a very long time, so I don't know the likelihood of them ever implementing it.

Also, I don't know if it's still the case, but it used to be that you had to not be on the move in any games to manually go on vacation, and players with a lot of games could potentially get into a situation where they never could go on vacation. The timeout protection could assist with that as well. 

However, all correspondence sites and organizations have their own rules that you have to live with if you want to play in their events. Some allow engine use and some don't, like here. Here, premium gets a perk of auto-timeout protection.

@4kingknight your vacationing opponent is playing 11 daily games, all of which are now paused - I doubt that you specifically are the target of a stalling strategy. Of course you are winning easily and so can justifiably say he should resign, but so are some of his other opponents whilst some games are still in the balance. Besides, at his rating it's probably valid to play all games to a conclusion for learning purposes. Your game has been going for about 8 days which is nothing for a daily game. The win will come eventually, you just have to be patient. 

OK, so it was another game which is now finished? 

So we've established that this is just the system working well (allowing people who for some reason don't have time to play to not play) and that it can be solved (just join no vacation events, which are every common). The only question is why do you even care? If they take a few extra days on a move or 2 it doesn't change anything, you can still play your moves whenever it's your turn.

I literally just started a game (1. e4) aganist this guy and he just did a 2 month vacation after being on 70 minutes remaining

Premium members are automatically placed on vacation when low on time in one or more games. They most likely won't take that much time but you can always abort the game with no penalty unless it's a tournament game.