Put the piston at BDC, feed some rope into the cylinder through the sparkplug hole, bing the piston back up towards TDC, put a rag over the hole to stop any shit falling in it (a valve collet once fell in there for me).
I lockwired the springs closed when in a vice myself, then put them back into place then cut the lockwire.
You can buy a special tool to do it which I brought, but it didn't work.