If you're willing to risk it, you could address some of the problem with your upper clamp bolt being above the top of the steerer by inserting a short length of steerer above it.

This is only to stop the clamp tapering off the top of the steerer; you'd still only have one effective clamp bolt. I'd only try it after reducing the discrepancy as much as possible with a slimmer headset and stem... is there any spare head tube / upper lug to remove? Plus, if you'd like a tighter head angle, you could shorten it from the bottom too.