I think that could work. I have something like that in my mod for Crocodile/AVRE. Though it is hard trying to convince the gun to engage the same target as the aiming-weapon.
This can be accomplished by increasing the value if I think 'last target' in target priority to a higher or equal value than suggested target. The idea is that the suggested target will always become the last target once move and stop commands are issued.
I'm not at a comp with mod tools to check, but I remember editing those values in such a manner did wonders for making turrets vehicles maintain targets while pathing. It's been quite a while so I don't kow how much those values have been changed since brits, if at all.