Just do a month long path clerkship in July, August, or September of your fourth year. I don't think ERAS goes online until September anyways so you should be fine if you can swing this. Just make sure you can get a LOR from the month-long rotation. Pick an attending, hopefully a cool one, and just sit in on signouts with him or her. Make it known that you're going into pathology and you'll be more memorable. The far majority of students rotating in pathology use the rotation as a blow-off rotation so if you declare your interest in the field early in your rotation, you'll be set. At the end, you ask that attending for a letter. Wabam! Done.
That should suffice. As for following up on the pathology on cases while you're on other clinical rotations...not worth the bother. Let's look at the following two scenarios:
(1) You would page the resident on the case to try to set up a time to go over the slides. The resident is busy as it is and would probably get all pissed off at you for bothering him/her. Seriously, on certain days, we can get paged by clinicians A LOT and it really gets in the way of our work. Please do not bother us so that we can get our work done efficiently and leave the hospital at 5 pm and have a great lifestyle. OK? When we find out that the person paging us is a med student, we're not really inclined to...you get the point. If the case needs to be seen by the entire team, well then the intern or senior resident can get a hold of us. Plus, when said resident shows you the case, that's not gonna get you any special exposure or attention from the department. The encounter lasts on a matter of minutes, at most. We won't remember you.
(2) Let's say you want to sit in on signout when the slides for your core bx or specimen is going to be looked at by an attending. Yeah, but you don't know when the particular case will come up. So you just sit in on signout while your intern/residents on the clinical service needs you on your clinical rotation to do scut for them. Again, probably not worth the bother. And it'll do wonders for your clinical grade when they find out you've been hanging out in pathology all morning long (just to follow up on one case).
Just do a month long rotation. Get one solid letter. Pathology isn't competitive. Shoot for the stars.
P.S. Guess I was rude and blunt...but hey, I'm just telling it the way it is cuz I don't want you to waste your time doing stuff that isn't gonna be all that helpful for you.