Denn, you have probably seen this but I found this excerpt on a DMV website -
6. I can't make the DMV Registration deadline, what can I do?
Go ahead and pay the DMV your vehicles registration fees and get your "half way papers" (Not valid registration, but an attempt to show responsibility, plus not be charged late fees). You may then explain to the DMV agent your vehicle's repair/smog situation and ask for at least a 30 day Temporary Registration Tag. You can post this Document on your vehicle's rear window, and drive your vehicle legally for 30 days or more, depending on the Temporary Tags you are given. In the mean time you need to attempt to resolve your vehicle smog situation.
Maybe a loophole you can use?
This is the way to go, I've done it myself in the past.
Just tape the red square in your rear window and you're good to go. Sometimes, if you catch the DMV person having a good day, you can get a 90 day extension. It's worth a shot.