Unfortunately, the collision check will work in both ways. When A hits B, B hits A in the same time. Even with logic, I don't see how we could determine which hit which. What you can do though is transfer a variable from one of the instance to the other, distinguishing A and B with a rule based on their instances (for example, let's says that A is the variable that was created first, so with the smaller UID).
I set up a little capx for example. You can drag the sprites to have the collision append. You'll see that the second instance is taking the value of the first one.
One last thing, if you want the collision to happen only in one way, you can "lock" the instances one they are picked up in the first way (toggleing a Boolean), and add a check on this Boolean in your collision check.