Try the following Elliot,
I heard of at least on precussion musicer and a numbers juggler doing the following before and after practice:
- Before: use a bucket with water as hot as you can stand. Soak your hands in it as deep as it fits and wiggle your fingers for up to a minute or longer if you can stand it. Now pull each finger gentle at first and more rigourous later. Your fingers will probably start to knack, it's okay. Let your arm hang and slowly start shaking them. Then lift arms arms perpendicular to the ground and angle your elbows 90 degree: think of youself as a young frigate bird and shake your arms, wrist and hands like wings till they are completely loose (sounds crazy but worked for Ricky Jay and me too...). Don't rush to it, extend the arms overhead and repeat in a forward backward motion. Flatter and shake them till they are completely loose and well circulated.
- After: use a bucket with ice water and put your hands inside for a minute or two, wait a couple of minutes and repeat. This will likely hurt like hell but it does help.
P.S. I know the shaking part sounds ehm strange but it does work for me. It's my usual warmup before I start some serious juggling or card throwing. The hot water bucket is easy to test, simply do only one hand and see if it makes a difference...