Sorry if you felt I was being unhelpful Meursault, I was trying to tread the line between saying nothing and laying it out on a plate. My suggestion about the 4 5-letter answers was intended to be helpful, given that we know the grid has 180 symmetry - it does however make the assumption that you have the answers to those clues and the 12's. If you do, then it is just a matter of finding a combination of matching intersects. With those in place, I found you could then start building on those 12 and 5 letter words - that is all that I did.
To add to my earlier hint (and touching on what Buzzb mentioned), my first attempt was to pair the 2 across 8's with the 12's, but this led nowhere. I can confirm that they do not intersect if that helps.
I'll get my coat now ...