For starters, as you know, each of those entries has: another idea, the one that’s in the grid itself, and they’re hellishly mysterious until you get the gist of this theme, which isn’t EZ. Most of the grid clues are pretty obvious – suspicious, in hindsight – and caused a lot of confusion.
For example, 63-Across, “avoiding something during awkward situations” is clearly “eye contact”, isn’t it? I can’t imagine an alternative. A handful of crosses confirmed this for me, except it just didn’t quite fit: CONTACT worked perfectly, but there were only two squares left at the beginning of the ‘eye’ input. ayyyyyyyyyyyyyyyyyyyyyyyyyyyyy I thought, I really hope this isn’t a rebus† I then moved on to 84-Across, “Fish With a Grab Tail,” and ran into the opposite problem. This should of course be “seahorse”, but now our thing is too short† HORSE works with his crosses, but there are seven squares left while only three are needed for ‘sea’.
It was then that I looked at the second set of clues (if I hadn’t I would probably still be scratching my head, though I bet people somehow figured this out without the help). “Leg cramps” is a pretty specific clue to a strangely called annoyance, the CHARLEY HORSE. Sure enough, this listing fits. However, how does ‘sea’ fit CHARLEY? I wasn’t quite there yet.
Frankly, the trick finally hit me in a reverse maneuver. I solved the grid’s clue for 105-Across, “Mad Hatter’s Social Event”, with no problem – “tea party”, which is two squares too short to fit in the grid in this spot. But I also had good luck with the down items here, mostly short bottom-of-the-puzzle fill, and completely resolved it on the intersections – THIRD PARTY. This matches “Unlikely Election Winner”, one of those seven secondary clues from the puzzle’s introduction. What’s happening here? Instead of ‘Tea’, read t† The “Expansion Pack” in the title is the second clue, which grows that t to a new word, tHIRD.
So, instead of ‘seahorse’, read C HORSE, that will be CHARLEY HORSE. Ah, and “eye contact?” that is l CONTACT, which belongs to the prompt “Communicate (with)”: lN CONTACT.
Using the remaining four entries G† O† B and p as their base letters. Like mr. McCoy says in his notes below, the puzzle had almost both clue components in the grid’s clue set; I think the trick would have worked beautifully in either case, but I agree with the constructor that separating them is really nice.