Similarly I don't think that I could adopt the brace position in a crash. I'm 6'6" and have a reasonably well fed belly!
Hands over head and leaning on the seat in front would be fine but most airlines that I've travelled on recently still have on their safety cards the leaning right forward, head near knees position which is just a joke for someone my size (and yes, I always read the cards, always check the exits, and always watch the briefings - even though I could probably recite most of them in my sleep!).
My big issue is what to do with my legs - they won't fit under my seat on most planes so I guess it is a matter of just havign them as far back as they can go. Which means that they would still be facing forward so at risk of snapping if we stopped suddenly.
Any suggestions?