Hey, Jim - I have the Cole jaws - and only have used them once.

When I first cut the tendon (or indent) on the bottom of a bowl, I
make a mark about the same diameter as the livecenter on the
tailstock. This can be done in many ways dependng on how the piece
is chucked.
After I've re-chucked it on the tendon and completed turning on both
the outside and inside, I usually give it a coat of shellac or sealer
while its still on the lathe.
Then I turn the bowl around and use a jam chuck on the headstock side
and bring up the livecenter to match the aforementioned ring on the
tendon as good as possible. If I did not leave a ring, I do trial-and-
error until I get it centered pretty well.Then I finish off the
bottom except for the wee bit under the livecenter - I undercut that
to about 1/4 inch with a parting tool. When I take it off the lathe I
carve off that 1/4 in diameter bit and sand.
The jam chuck can be most anything. The chuck with a piece of 1/4 in
foam over the jaws. A piece of wood turned to a diameter smaller
than the bowl edges but larger than the bottom. A vacuum chuck
without the vacuum. Don't bring up much pressure with the tailstock
and take very light cuts,
This is the fastest way for me - - and I can handle bowls up to 20in
in diameter (my lathe is a 2036). Most of my bowls are not
completely dry - so they move after turning and are somewhat
elliptical before i get to the bottoms. If I relied on Cole chucks or
equivalent edge holders, I could not work these.
This method also works just as well with natural edge bowls!