[FattyBoomBatty]

Can't you just plug the battery in, and the starter wire, then take a screw driver and bridge the positive battery cable on the starter to the solenoid spade, make pretty sparks and get the nut off.

Also, it could be the air hose you are using. A smaller diameter one acts just like an oil restrictor for a turbot. Get a better hose, try again. Just borrow, don't buy, I should say. All you need it for is one nut.