The easiest thing to do might be just to put a pot under the runners and let them root themselves. They're very good at it!

I cut the runners off and using bottom heat obtained a new plant from each node on the runner. To do this I peeled back the sheath to make it easier for the roots to get to soil. So I would suggest you let the runner grow as many nodes as possible, then at the end of summer you can have many many baby plants. Then you just need a cold frame to nurse them through the first winter !