OK, I'm going to put an entry in for this one.
Only thing is - how to get to the start? It's 2 hours 20 drive according to AA routefinder so that would be lieaving home around 2 am. It's shown as 194 km, so with one suitable control that's 200 km to the start, so the sensible thing to do would be ride to the start Friday night, have a kip, do the ride, sleeping at Glyndyfrdwy (345km), and a leisurely ride back. Last control shuts at 10 am, so should be home early Sunday evening, well within the time limit for a DIY 800.
Does this sound like a good plan or have I finally lost it?