Cant you make it so that you DRIVE in 1st person?
I know that if you're using Skys the Limit, and you get in a vehicle and push the 1st person view button, then you'll be driving in 1st person!
Now it looks completely wierd in a regular warthog... or any other vehicle for that matter... but you can make a warthog, that, when you do the trick mentioned above, will put you in 1st person in the driver's seat. I think that warthog is in the map "Mini Stunt".
Go check it out!