A subject dear to my heart (see my recent posts).
You need a 22mm hex driver. Your choices are (1) a 22mm hex driver - I haven't been able to find one for sale (2) a 22mm allen key which you cut (creating a 22mm hex bar which can be slotted into the axle and fit a 22mm socket on the other (for torque'ing purposes)) (3) a 22mm bolt head welded onto a socket (4) a £45 BMW kit which includes a box wrench with a 22mm outside hex fitting (5) finding some 22mm hex bar and cut a piece off or (6) and what I have done is to buy a special motorcycle tool (that's how it's listed) from Snap On (cost circa £20) with a 22mm outer hex fitting and a 1/2 ratchet fitting.
Hope that helps.
Regards, Will