I don't have one in hand yet... delivery hasn't arrived...
However... it should be similar to the first based on the user manual of the mkII.
1. Menu, Custom, A1, AEL/AFL menu
2. Select S-AF Mode
3. Set the option to mode 3
4. The go to your buttons menu under Custom Menu, B
5. Select Button Function
6. Change FnII to "AEL/AFL"
That should now do it for you. I assume. It seems that way from their user manual...which is certainly not the most helpful.