Hey, John!
Lon Rombaugh is one of the best grape growers in the country (the
author of the only organic grape growing guide as well). I found his
page on rooting grape cuttings - see if this is helpful:
http://www.bunchgrapes.com/cuttings.html
My husband, Rob, and his Dad actually started our original nursery
business rooting grapes - they simply stuck pencil width diameter
cuttings in the ground with two nodes down and one node up. The
bottom of the cutting was cut straight across directly below the
bottom bud and the top was angled about 1" above the upper node. No
hormones, no special stuff - ran about 80%. Straight into the rows in
the dirt (and you've heard me cursing about our "dirt" - heavy clay).
They didn't even particularly water them. If you are planning to use
a potting medium, you would need to maintain some dampness. Our
favorite rooting "mix" for almost everything in the nursery was 50%
perlite, 50% vermiculite. Sterile, well-draining but with good
moisture retention and aeration.
The auxins released by willow cuttings are a long-standing natural
rooting agent. Some folks actually chop up the willow shoots (or
roots) in the belief that more of the hormones are released that way.
I've never seen anything definitive.... but perhaps googling around
will turn up some Official Study about it!