I don't think an apple root stock would work as its not closely related. Additionally, theres a technique called budding[1] where you just graft individual bud

I don't think an apple root stock would work as its not closely related. Additionally, theres a technique called budding[1] where you just graft individual buds. This has the advantage of maintaining the habit and structural integrity of the root stock. Haven't got any good resources for you though, sorry. [1] https://www.rhs.org.uk/advice/profile?pid=400 https://www.rhs.org.uk/advice/profile?pid=400