After many months of trying to talk to someone who runs their IR Defense MKII 35mm in Clip-on mode with an ACOG or ELCAN, I finally am working on it at long last!
It certainly is much more difficult and time consuming to zero the MKII to the day scope than my T-70/T-75s are, but where there is a will there is a way.
First off, you will need a rock solid AR-15 magazine well mount to place your rifle in so that it does not move while mounting and removing and remounting the MKII thermal in front of your day optic.
You first adjust your day optic onto the target bulleye at the range you have your day optic zeroed.
Then you carefully attach the MKII in front of day optic on the rail as close as you can without moving the rifle off target.
Fine adjust the MKII ocular diopter to get best focus after you've turned the scope on.
Go to Level 4 by turning the left turrent.
Turn the right turrent to CO for Clio-On mode.
Turn the left turrent to Level 5.
Use the top and right turrents to shift the entire scene until your day optic is back on target.
Turn the left turrent back to Level 1 to save the setting.
Remove MKII and insure day optic is still on target.
Reinstall the MKII, turn on the power, go back to Clip-On mode from level 4 and make sure that the screen position was saved and the MKII is still on target.
If not, repeat until on target.
Take some practice shots at the range at which you originally zeroed your day optic and repeat again to fine adjust your zero.