the image doesn't work, could you reupload? I'm thinking about making myself one of these as well. Thanks!
Epiphany!!!! Use a bike hand pump, disassemble so it's just the handle, shaft, and the actual pump. Take off the handle and foot rest thing, so it's just a tube with a metal rod. Drill out the outlet so it's wider, and there you go! Just get a bow and find a way to mount