The only variance is that when doing a "Cactus Jack" you wait for partial numbness to restore until you feel the "Pins and needles" in your hand. You then masturbate and it feels like you're jacking off a real cactus.
Other Notes: It does not matter much if you reach climax during this as real cacti retain liquid and cannot orgasm.
Should you jack off a real cactus please seek immediate medical help.
If lonely in the desert, take a small cactus and carefully remove all needles. Insert a knife in the bottom and hollow out the pulp. You should now have a flap of cactus skin with a nicely lubricated, aloey, gooey lining. Carefully insert two fingers and feel around the inside looking for any "ingrown needles". Once satisfied that your cactus meets all safety requirements, you may proceed to have sex with it. Afterwards, rinse and repeat as desired. The flap will fold easily and can be kept discreetly in your pocket.