If you really feel that a lock is the only way to keep you from the desserts, the least expensive (and bothersome) solution is probably to just get yourself a simple metal lockbox (available at most discount department stores like Target, Wal-Mart, K-Mart, etc) and ask your husband to hide the key somewhere.

I don' t know if there are any pre-existing solutions out there for a programmable lockbox for the freezer (and if there are, they would probably cost quite the pretty penny), but there are programmable safes around--a little pricey, and I don't know if the cold of a freezer would effect their performance. If you know anyone who is moderately adept with programming and has a basic knowledge of electronic hardware you might be able to sweet-talk them into doing some custom work for you.

Good Luck!