I'm using a wooden kebab skewer here. I wrapped a little bit of sticky tape near the top to stop it sliding out. Seems to work mostly well, but I think the thinness of the tip stops it from registering sometimes.
I can't quite see myself walking through a local knitting store, but might look at that. I'm sure noone will ask questions of the funny guy trying to put knitting needles into the electronic do-dad, will they?
I assume you can buy single knitting needles, or do I get a spare stylus "for free"?