You can subsribe now and cancel it right away to get the january bundle.
I would so be throwing likelys around in regards to getting alien (though in your case I think you are just saying buy it and cancel and still get the bundle which is cool, but realized after I made this post >.>)
as I said the wording is different from all of their other promos trying to get people to get signed up (the previous ones asked you to subscribe this one is saying pay now as in paying early for it compared to a week before)
vs
completely possible they are trying a different tactic to keep more subs by either letting people get extra games by paying early and constantly subbing, or trying to get money earlier by having people pay for the next month and get a game early from the next bundle by giving them money early.
there is no grantee that the game is in the bundle that unlocks tomorrow, it's just likely that it is and the promo was poorly worded and not supposed to be on a sub's page, but giving the apparent drop off in subs between the first and second bundle it wouldn't be surprising if they were trying new tactics to keep people.
I mean offering a valuable every so often for people who are current subs but not available to people who weren't would be a way to keep people subbing more constantly so they don't miss out on those.