E,
I sometimes get excessive bleeding, flooding the grafts.
Don't know if grafting 'by the signs' would help, but I pretty much have to do 'em when I can steal a few minutes here and there to get out in the orchard.
I've had old-timers recommend beheading the rootstock - and waiting 'til they stop bleeding before grafting - may take one day, or a week or more.
Another technique which I use frequently - though I can't swear that it necessarily works any better - is the 'Sap-stopper modification of the Gray Graft'. Essentially, it's a simple bark graft - but instead of completely beheading the understock, you just cut about 3/4 of the way through and 'break over' the still-attached top, to act as a sap-drawer or 'relief-valve' of sorts.
Did a couple this morning, but it's still a bit early on many of my seedlings - look at Dr. Reid's most recent post.

In grapes which bleed like bloody Mary, I believe they make a cut below the graft to bleed off the excess sap. That might be worth a try. But I have no real experience on either.

The guy who taught me to 3-4-flap graft does a couple of incomplete 'girdling' cuts just below the graft - not removing any bark, just a quick couple of knife swipes most of the way around the stem of the rootstock; they callus back across, but I guess also serve as a 'relief' valve of sorts - and probably also help to keep auxins concentrated above the girdling cuts to augment callusing.

Thank you both for the feedback and advice. Lucky, I grafted a couple black walnuts yesterday and tried doing the 3/4 of the way through and break over still attached thing. Thanks, Eric