Sealing tub spout against tub surround?

[ryanwj]

I have a Moen tub and shower faucet in a new basement bathroom I just finished and the last detail I am concered with is the seal where the tub spout meets the tile surround.

I was surprised to find the tub spout screwed onto the nipple and the length of the nipple determines the standoff of the spout from the surround - I needed an odd size nipple that I had to order from Mcmaster Carr, but I finally got the spout to seal the NPT threads before it hit the surround. Now I don't know what to do where the spout meets the surround. Any advice? Plumbers putty in the opening between the tile and the nipple maybe? Surely caulk is not the pro solution here.