i'm going to be trying this, i've never really considered it before....
i have a collection of cacti grafts of various species. i graft cacti for several reasons, often a species is intolerant of water and the rainy seasons here, and will rot outdoors. grafting to a water hardy stock solves the problem. another example is smaller slower growing species that take 20 years to become noticeable sized can achieve the same size in three years on a fast growing stock. with cacti, humidity is key as the graft heals. i would assume the same for this, so a wrap of moist paper towels and saran may help, and a humidity bag would be needed i think...
another thing i think would be necessary (going on whim here, no research involved

) would be to line up the vascular bundles (the water pipes). if there is no connection, there is no transfer of fluid, and the scion dies...
ok, going to see what i have to work with in my run down mite infested basement....