I used a set of bolt cutters
Bit agricultural, but it did the job!
Used my keen powers of estimation to work out where I needed to cut it off, then cut it off a bit higher than that (easier to cut more off later than put more back on

)
Use the bolt cutters a bit like a tube cutter- work your way around the outer tube gradually cutting deeper and deeper as you go. Eventually it'll kinda "snap" at the weak point where it's cut. Make sure that the tube is not squashed around the shaft after it's cut, if needed use some pliers to carefully reshape it.
DO NOT BEND THE SHAFT ITSELF! It'll catch inside the outer tube and jam up... not good.
To cut the shaft itself, I pressed the shaft down to it's stop point and used the bolt cutters to cut it about 5 mm higher than where the outer tube was. The thread on the end of the shaft wasn't needed.
When it's released again, there's just enough room for you to have the shaft sitting between your fingers (Stops metal filings going down the tube) while you file down the jagged bit left by the bolt cutters. End result is about 3mm clearance from the cut in the outer tube when it's pushed down to it's stop point.
I cut mine again after trying the knob on it to get it just right. Same procedure again.
To finish it off, I found a small rubbery plastic cap that fit over the end of the shaft just to eliminate any chance of noises from it.
Adjustment is simply a matter of raising or lowering where the knob sits on the shaft (please refrain from any sexual jokes here...) to have the button sitting on the end of the shaft without really pushing it down. You'll feel it when it's right.
Very happy with the end result, looks the goods and feels like factory equipment.
Hope that helps...