The path of least resistance is a variation on my earlier comment. Remove the wall in front of the garage door, but leave the wall between the double garage and the single garage since that wall does not preclude the single space from being used as a garage. You would then have the required 3 car garage, one space of which is used as a bonus room but could be used as a garage when you decide to get a Smartcar or Fiat.
All that said you may want to talk to your Attorney before proceeding.
Broker / Owner / Architect
I can't honestly tell you that I know for sure what the building and planning department for Danville will say when you request to do this. I do know that you really really really should not do it without going through the formal permit request process. There are all sorts of legal and insurance aspect reasons why it must be done "on the record."
I just closed a deal in Brentwood on a 4000 sq ft house that had a split garage in which one portion was a 2 car set up and the offset side was a one car stall. Before the buyer made the decision to buy the house we went to the planning dept and asked if that 3rd stall could be converted to living space. Brentwood said YES it could as long as there are at least 2 stalls remaining and the process was done with permits etc. This seems to be a common answer. Most cities don't want large houses with little or no garage parking available as this causes everybody to park on the streets and can cause visual blight. Danville might have a different answer. The best and only way to to know is to go down there (or call) and ask them. Good luck!