The Christmas Tree Coercion

"Okay, so I had a brilliant idea while I was at work today, and you can shoot it down if you like, but I think it has a lot of of potential."
Show him you value his opinion. Let him know you'll decide together.
"I noticed today, while I was getting supplies to make Christmas gifts for our female relatives..."
Nice, show him you're a team player.
"That the Christmas trees are on sale, 50% off at Hobby Lobby."
Thrifty! Now you're on fire!
"So it occurred to me, that, since this weekend is the last weekend that we will get to spend together, just us, before the wedding..."
Appeal to his quality time needs.
"We should go get a small tree, decorate it, and have a little early Christmas! You know get in the holiday spirit AND start a fun tradition for things we like to do to get ready for the holidays. The things we do this weekend could help to build the foundation for what we do every Christmas in our marriage."
Closing statement listing pros and validating idea. Perfect!

Give her the look, make her think this could go either way.

"What time does Hobby Lobby close?"

"Eight."

Look at clock...sigh for effect...
"Okay, get your jacket. Let's hurry up and get over there."

"THANK YOU! I'M SO EXCITED! THIS WILL BE SO MUCH FUN!"
Mission Accomplished. Throw self into his embrace.

Mission Accomplished.