Well you could turn the garden hose on em and if he doesn't like it and comes out with a screw driver then shoot em.
Also I think here (La) technically you would be legal but still wouldn't look good on your part so much, you could jump in the car with him and then shoot him since he made forced entry. Though it would be hard to convince a jury its not bloodthirsty premeditated homicide since in this case you knew he was there.
La RS 14:20
(4)(a) When committed by a person lawfully inside a dwelling, a place of business, or a motor vehicle as defined in R.S. 32:1(40), against a person who is attempting to make an unlawful entry into the dwelling, place of business, or motor vehicle,
or who has made an unlawful entry into the dwelling, place of business, or motor vehicle, and the person committing the homicide reasonably believes that the use of deadly force is necessary to prevent the entry or to compel the intruder to leave the premises or motor vehicle.
No stipulation on you being in the vehicle when the entry is made.
http://www.legis.state.la.us/lss/lss.asp?doc=78338