I would think you just screw them on but i am not really sure. I built my own bc wheel out of a bmx tire and i screwed wood onto the bolts on the sides. It was really fun and it worked fine till i jumped one time on it really hard and one pedal broke. What i am trying to say is you can make your own pedals out of better material then i have, but for your question i think you just screw it on.
You’ll need a beefy axle for your BC to work well. One way to find out if your is, is to try it and see if the axle bends after a while. I bent my original axle with my old BC (many years ago), but my local bike shop was able to replace just the axle while keeping the same hub. The replacement was a 14mm axle, I believe. Thinner ones may not hold up.
ok thanks for all the advice. But the idea of breaking my axle then not being able to use it has put me off the idea because the wheel is off a really cheap bmx. I will save up and buy a proper one. thanks again for the ideas.