How to do approach grafting on 2 unequally sized branches?

[Samu]

I have a few couple candidates to do this kind of grafting, but not sure on how to do it properly.
I buried few seeds next to a more established trees for purpose of doing an approach grafts in the future; thereby making the trees essentially a double root stocking ones.

Spring is few months away, I thought I better prepare myself and do it correctly. (or, does it matter what season?).  Meanwhile, the seedlings will probably be about pencil thick, while the more established trees are about large broom handle sized or even larger currently.

In short, how would one do the proper cuts in order to mate the skinny branch to the larger trunk? I've seen videos and drawings of approach graftings, but I have yet to see how to do it on uneven sized branches...?
I guess my worry is that, the cambium alignment thing... I am pretty sure is being done, would anyone share the proper technique how this is accomplished?
Your help is greatly appreciated...thanks!

[rliou]

The technique for lining up he cambrium would be similar to veneer grafting except u dont actually leave the little piece at the bottom to hold the scion.  I find it easier to tie two branches at a few cm above and below fhe cut which makes lining up the cambrium easier.

[Samu]

Thanks Robert for taking the time to reply!
I've since been googling some more, I think I'll try to do the following method:

Score the stock's bark to approximate the scion's size, and peeled it up a bit but without breaking it; then insert the scion underneath it.
I don't know what this kind of grafting is called, since doing it this way one needs to cut the scion (just as you would do on a regular cleft graft); but the benefit is, if it doesn't take, the seedling will still be alive and can reused...
So: it's like "bark grafting" method with a live scion (seedling), but for different purpose...