Boards up, weight back. Make sure your main traveler is centered, and sheeted accordingly. Too much twist in the main will force the bow down when you slow down from the bow stuffing, making matters worse.
Raising the spin pole could help too. Turns some of the forward pull into lift, but at the cost of not having as much speed. I never tried it on my FXone because I didn't know that until after I had switched to a different boat. You'll have to adjust the luff tension as well. I don't remember how the bail was rigged on that boat. I'd ditch the wire bridles for the spinnaker pole and just make them out of dyneema. I'd probably switch attachment points as well from where the main rigging attaches, to a hole in the bow. Better angles, less line, less load on that single point as well.
Trapezing downwind helps a lot to keep the bows up.
The toughest thing about single-handing a spinnaker boat in bigger wind is that you do not have enough weight, or leverage to really get the apparent wind forward when going downwind. Every time you slow down just a little bit the wind is coming from basically straight behind you, once again, making matters worse.
Don't pull the boards up all the way though. I tried that one day screwing around, and those flat bottom hulls will just skid every time you twitch the tiller. That is an odd, creepy feeling having a boat slide.