I was in PNP in Nov, cold was snowing and cold removing the Pressure Plate off a 81 Euro W123 300D. The last bolt of the 6 had the head already stripped.

Did I mention cold? and it was closing time, and a 617 38# FW was almost mine.
Bought the 4 bits set of Triple Square from O`Rileys. come in 6,8,10 and 12mm. With a Hammer I drove home the 8MM into the head of the bolt and she came right out.
Don`t know how much room you have, but this could work for you.
Charlie