So I had one tube that had ripped open because it was pinched between the tire and the rim, and one tube that the stem top had come off because I had the pump head closed when I pulled it off. I took pliers to unscrew the stem top of the first tube and let the valve fall out the rip. Then I poked the valve through the other tube just behind the stem and dropped it through to screw the stem top on the other side. After patching up the hole I poked through to get the valve in, it seemed to hold air! Voila!
Now the question is: How dependable is this repaired tube? I'm carrying it as the second spare just to be safe.
Main concern would be rate of air leakage at pressure. Only way to tell would be to mount it up and pump up to pressure and see if the leakage rate was acceptable over nite or a few days. If you have already checked the blown
tube for adequacy of repair use it for a spare while you check the repaired valve
I rode a tube that leaked 5-10# hour for awhile before taking time to pull it and
find the pinhole. OK for short rides.