Clamping featherboards to my tablesaw was always a hassle until I discovered locking welding clamps. Their C-shaped jaws adjust to fit the webbed castings on the bottom of the extension table. They clamp and release easily, so adjustments and realignments are a snap. I use locking welding clamps all over my shop. They're much lighter and easier to use than long-reach woodworking clamps. Be sure the ones you buy have swivel pads. I glue on plywood faces, for no-mar clamping.
Seven Corners Hardware, (651) 224-4859, www.7corners.com, Vise-Grip locking clamps w/swivel pads, 9SP, 4-3/4-in. throat depth, $20, 18SP, 9-1/2-in. throat depth, $30, 24SP, 15-1/2-in. throat depth, $38.