You can still do it Paul.
The Regs state that there should be a maximum of 2 metres from the cooker to the isolator. (Wall switch - double pole.)
All you need to do is fit another isolator/switch in a cupboard where you can easily get to it. That way, you don't need to alter the position of your original wall switch.
Cable length doesn't come into it. It's a matter of accessible isolation.