try what the other guys said,,,if that fails....

find a GOOD engineering shop and they should be able to install a hellicoil...basically a steel insert, they drill the hole overside than wind the tapped steell insert into it, done VERY commonly on spark plugs that people have stripped in alloy heads (please dont ask how i know so much about it its embarrasing..)

wiht heads it can be doen on the car, but its better to take the head off due to the difficulty in clearing any chips that fall into the cylinder, with a oil pan thats nto a worry as it can easily be flushed with a gallon of cheap and nasty oil afterwards...

you WILL need to find a proper automotive engineer to do this though your local fast change oil shop will thinkk your talking martian...