Ouch. I personally would not have stuck the thumbtacks into the trunks. Here is what I did:

{{gwi:23126}}

Wrapped in grafting tape, held secure with zip ties.

I left my zip ties on to long and they cut into the trunks. Cuttings where wrapped in the crease they caused and are being held in place by the tacks.
In bonsai focus this was done by one of the bonsai masters in Bali.(?????)
I'm hoping it works,