I don't think it's possible, and even if it is, it would be a lot easier to do the work with the pump off the car.

Where are you located? I have a piston-style pump that I pulled for my 240D but found it not completely compatible. I'll sell it for $20 plus shipping.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.