One of the first few quiet walkways on the WPLP has good access. You can walk out onto the riverbed under normal water levels without getting in the water. It is pretty open as far as trees go. It is pretty low in elevation, so it may be a bit too warm right now.
A cane pole might be good for him. Attach a leader and he can still get some reach without the tangles and hassles of casting a fly rod.