Why not make them bottom to replace your current bumps? I got a little carried away when I drew them up and have around 6in of travel... I think I going to scale down to about 4.
As for dampening I'm hoping forcing the air through the holes in the piston will provide dampening. I think me and the op are on the same page with thag.
I'm going to experiment with different piston set ups and using air, air/light oil, and pure oil.
That won't work. You won't have enough volume of air to dampen anything. If you want to use just air, don't put any holes in the piston. This will compress the air and become more stiff the further it travels. Think of it as an air cushion. You can tune the compression with air pressure, but you cant tune your rebound. You also won't need a coil spring in there. This is what they are building in that pirate thread.
If you want tune-ability, with holes in the piston and a shim stack, you need an oil. This is what Fox, King, Bilstein, Profender, FOA, etc use.