I want to start with saying i have 0 experiance with yangmei. So if what im suggesting here is a bad idea, p[lease correct me. (i clicked this topic because i was curious what kind of fruit Yangmei was)
But if your grafting with a large size mismatch, my mind goes to chip budding.
This topic is about how to chip bud with large size mismatch between graft wood and rootstock.
I hope it helps.