I've done it: Now I just have to code in a HUD displayer to show its charge and something relative to Boots/Armor/Flags, which will change its use.
It'll recharge itself when not used, and will be an optional Starting Item. To activate it, you must be in middle-air and hold the "Crouch" key. As far as I'm concerned, there're no bugs, but the bots won't use it (they always follow their pathnodes...). At least we may use it thoughtfully :rolleyes:.