Ever heard of grafting different rootstocks together (other than fruit trees?)?

Yes in Roses, Melons.By mechanically grafting the commercial scion onto a more vigorous and resistant root system from a hybrid plant, the plant will develop many traits that will withstand the root infection and subsequent drought stress.

I've only seen this with fruit trees (multiple citrus types grafted onto a single rootstock) -- I'm sure the same principle can be applied to non-fruit trees.

Rootstocks are usually chosen for vigor and resistance to soil-borne disease.

Grafting is a fairly precise procedure. While common in fruit trees, grafting is not wide spread. BUDDING is done commercially to produce many ornamental plants. This process requires a compatible under-stock (wild-type under-stock for a desirable stem). This is something NOT for the untrained. The under stock and bud need to be closely related (Same family), rubber bands and wax are generally used

You can do this with different species within the same genus, (like apples to apples) but you can't do cherries to oranges. I think I remember years ago seeing a catalogue where you could get a grafted tree with different kinds of citrus on it, but I don't remember where it came from and a quick check of the internet didn't turn it up.

Grapevines are ALL grafted onto a different species' roots.

cucumber-pumpkin-melon (the same family)

Nerium as a rootstock for adenium

various species of cactuses, aand succulent euphorbias

all i can think of off the top of my head.

good luck, i would start with the cactuses (or cacti?) if i were you

try it, you may invent something