ive just fitted some usds to my nc30 the top yolk is a one of with no mount for the ign switch has anyone fitted remote ign to their bikes or know of a small enough switch that may fit into the stem which is 28mm cheers

If you're willing to extend wires then you can pretty much mount the ignition switch to wherever is convenient for you. I don't think that mounting it in the yoke stem is a good idea, too much movement and no way to fix it (very) securely. It might be easiest to fabricate an ignition barrel adapter and fasten this to your top yoke.

The ignition is really just a simple switch that uses the key to move its position, there are plenty of other alternatives (i use the kill switch on my racebike).

A stem-mounted ignition switch is a nice idea but I couldn't get it to work very well, on an old rat bike I used to try these things on.
Like Cammo said, there's just too much movement involved for the wires to deal with.

On my NC21 I'm using a battery isolator switch, on one of the sidepanels...