Hmm I see, the problem is that the valve is at the fwd end of the robot, just under the flipper plate. To the side there's no access, so it can either be the bottom (easiest) or through the flipper...which is not ideal as I'll have to tear quite a large hole in it!
Might be wrong about this, but I think there's no danger in having the robot upside down as long as the flipper plate is locked no? What I mean is, you have the robot disconnected ( link removed so no elec power), flipper arm locked, so when I open the valve nothing should happen. Then I put the robot upright, insert the link and power up, and finally remove the locking pin... would that be an acceptable procedure?