If you just must do this… You can make yourself a patch cutter and produce many patches fast. Purchase a short peace of iron pipe found in the plumbing section in any hardware or building supply store with an inner diameter of the size of patches you prefer. Grind or file a knife-edge on the outside end of the pipe. It needs to be sharp and even so patches are cut nicely. Prep the old tube by sanding and cleaning with alcohol. Coat with a very thin application of rubber cement and apply wax paper. Wait for the cement to dry then place rubber on a peace of scrap wood and place the pipes sharp end down on the rubber. Hit the pipe with a hammer producing a perfect round rubber patch. Cut as many as you can from the prepped rubber. When applying the patch clean and prep the leaking inner tube as normal. Pull the wax paper from the home made rubber patch and coat with rubber cement. Allow cement on patch and inner tube to dry, press and hold firmly in place while cement cures.