Gift
Buying a firearm as a gift is legal, and not a straw man purchase. One has to follow the rules for the paperwork, but if done properly, it is entirely legal, everywhere, under federal law.
You may have to go through some additional paperwork under some state laws to ensure the recipient of the gift meets all state laws (FOID, pistol permit, etc.), but there is a legal process for doing it.
Not all dealers are as aware of the details as they could be, but they are aware of the danger to them of allowing "strawman" purchases, and will shy away from anyting that looks risky to them, so you may have to do some explaining to make them feel comfortable. And do it up front. If a dealer is unsure, have him look it up. Once he is familiar with the rules, and which paperwork must be filled out (and how), you should have no trouble.
If you want to avoid any appearance of impropriety, simply have wifey give hubby the cash at home before going to the gun shop, or have wifey (who meets all the legal requirements) buy the gun herself, filling out the forms herself, and then give it to hubby later (like under the tree).
As long as hubby is legal to own the gun (and state laws are also followed), there should be no problem.