Sorry dont no but be interested on this.

It doesn't have to be just apple trees either, a lot of trees are suitable hosts if you try it
!
The way to go about it is to just break open a small part of the bark slightly and push a few seeds into it and try and cover it back over, it takes a good few years to develop but it's a good long term investment.

This needs to be done in February when the seed has matured. I don't think the berries in xmas mistletoe are mature enough to germinate.

Just do what the birds do and wipe some ripe seeds along a branch - cracks and crevases are good for holding onto the seed, especially if we have any heavy rain. I would resist cutting into the bark for this, especially as apples tend to have lots of their own fissures etc.