I decided not to cut mine and bought and extension, but I attached a magnet to the crank ring and cable tied the sensor close by and rode like that until the extension arrived, only issues were speed was out obviously and no speed cut out.Thanks for the suggestions. The handlebar mount looks like it could work if grinding the paint off the bars doesn't work.
If I choose to cut and extend the cable is it obvious which cable attaches to which when reconnecting, ie are they different colours? I have a fear of cutting the cable and then reconnecting it wrongly. Although with 3 cables it won't take too many tries to get it right..
Cutting and joining may look neater as there would be no connector bulge and if you have heat shrink to match the cable it would be hard to even see.