- Just solder or crimp a chunk of #12 copper wire and bend into a hook or ring or whatever. Then just hang them up on something.
They may dent the vinyl a little bit, but they won't have the pressure to cut it. I guess if it did you'd just have to cut 1/2" off your tube.
EDIT:Test tube clamp:
You could bend it 90 degrees just before the jaws to get it to hang vertically. And they're less than $1.00 each with 12 or more...