set your e brake, don't start the car, but put the car in neutral, that should free it up for you.
Also, rocking the car forward taking up the transaxle play and using the ebrake or tire stops to keep it forward. I found if possible parking it on a slight down hill makes this easier.
[TRADED] 2005 Grand Prix Silver
K&N Air Filter, NGK TR55GP G-Power Plugs, Delphi OE Wires, Timken Bearings, Mobil 1 Synth ATF & Oil, Purolator PureOne Filter