Hacksaw mate. The other way is to drill down the centre until it just breaks thru' into the stick and tap it out to M10. Screw in an M10 caphead and just keep tightening until the reverse action of the screw lifts the old knob off the stick.
Tools needed: 8,5mm Drill, M10 x 1,5 Tap & Tap Wrench.
;-)