Easy, but who gets you out again?
Before you go in under the dash, just park the car on a slope facing downhill and tie a length of rope to your ankles, secured to something handy like a lamp-post. Tie a longer rope to the car, secured in the same way.
Then when you have finished work, just get a passer-by to release the handbrake. The car will roll forward until arrested by its rope. Meanwhile your rope, being shorter, will draw you smoothly out of the footwell, depositing you on the road behind the car.
Simple!
