One thing that may help is pulling the wheelchair instead of pushing it. This might be a little unsettling for the rider, but the big wheels in back are less likely to get snagged on bumps, debris , big cracks in the pavement or what not.

If the person has the phyical capabilities, perhaps one of those sit down hand pedeled bikes? That's probably a stretch though.

Not sure if that is any help, but thought I'd chime in anyway...moved a lot of wheelchairs in one of my jobs...learned a few tricks.

For short distances, if there are people strong enough to do it, the wheelchair can be carried by two or three people with the rider still in it...don't trip!