Great minds think alike!
Funnily enough, my other plan was, either from the summit or after the Gribin, going up Lliwedd, then dropping down from Lliwedd Bach, past the mine levels, and down to the mining track that skirts SW back to the Watkin. Alternatively, going slightly further round the ridge, then dogleg back down that slope. It’s difficult to tell from google earth, and you don’t really know the surface is like. I seem to remember a couple of guys from one of the magazines tackled that southeastern quadrant.
There’s almost certainly a viable route, as that part of Lliwedd is generally quite grassy, but it’s potentially quite a tricky 200 or so metres.
As it was, after descending to Glaslyn and back, I didn’t really have anything in the tank to go up Lliwedd. It probably adds another couple of miles to the length as well. I’d be interested to hear the best way of tackling that section.