Don't see any good reason you can't add a longer hose. Will take a few more pumps to pressuize the hose, and you'll get more air bleed off when you finish pumping, but it shouldn't make any differnce.
usually my rifles are transported to the firing line in either a hard case or a soft case. Will lay the case down on the ground. When time comes to refill, will just put the gun either in the hard case or on the soft case, then fill it.