You can do this in the default keybinding interface, can't you?
"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
As far as I'm aware, you can set shift to something alone, but you can't alter the "modification" ability of shift itself. OP is looking to make Ctrl, Alt, and Space to be the modification keys while Shift is jump.