Store to tag history on previous value greater than current value? and no other situation?

Through Tag history, is there a way to only sample a value when it is less than the previous value?

So say, a int tag is at 7521 and goes to 1. I want to store 7521 with a timestamp, not the timestamp of: 7520 or 1.

I am trying to put this into my UDT. Not use a transaction group of some sort or on change events… If possible.