i have done some root grafting on both tiny and larger scions.
If had best success letting them “heal” in coco-peat. (just enough moisture, that if you squeeze a handful only 1-2 drops of water fall out) in zip lock bags at room temp. And than planting out.
I have to warn you though. They are sensitive. I forgot to water them once during a dry week. And they all died. Where my just planted grafted rootstocks did fine.
if you have tiny scions you could also try and chip bud them. If made a topic about that here