The mould I used is a 3/4" PVC pipe coupler. Sand down the inside to make it smooth, helping to release the cast when hardened. Use tape to keep the gypsum from leaking out. The saw cut allows for prying the mould open with a screw driver, you should be able to push out the cast easily.
After connecting the wires, isolate the external electrodes and connections with liquid tape to make sure that the there is no external parallel electrical path.