As far as I know all budding should be done in summer when the trees are in active growth. I think you may be better off pinching the top of the whip (im assuming its a whip with no branches).

Ive thought about this as well and I thought about pruning to an open center with 3 or 4 scaffold because it makes it easy to get those scaffolds as different varieties in a ew years with cleft grafting. Not saying you couldnt do it with a central leader/MCL just that in my veiw it makes it easier to differentiate between the grafted branches. It would (assuming) make larger branches of thse varieties in which you want to graft (open center) where as an open center, you would have to either graft the entire top with one scion, wait till it branches, then graft the wanted vaieties on the whorl.

I just woke up so im sorry if it is a bit confusing lol