I tried this in the middle of the growing season using some random late-sprouting bines on my Centennial, Chinook and Cascade plants. I just buried them under a couple of inches of the leaf mulch from the crown out a couple of feet, leaving a foot or two of leafy ends.
Two weeks later they had all sprouted hundreds of roots up to a couple of inches long. I could have cut them and planted them but with 15 two year old and very productive plants taking up all the prime real estate I would have had to make a new bed for them all...
Cheers!