Hi,
For the bypass valve you can use something like this:
http://www.ebay.co.uk/itm/BMW-Mini-C...item4d2bbd49cf
You CAN drive the car perfectly safe with permanently engaged S/C magnet. Stock it's engaged permanently after ~1500 RPM.
If you want entra power you should use bigger crank pulley and/or smaller S/C pulley.