At his weight, a back carry really is best, ergonomically speaking :)
Have you tried hooking some toys on to the strap with him in a back carry in your Ergo? Maybe that would help him leave your hair alone. The Scootababy really is the best hip carrier around, but it's only really good for a hip carry and I don't find mine that comfy for long periods of time with dd who is 24 lbs.
The only other thing I can recommend is a good woven wrap or a toddler carrier more suitable for front carries. My daughter actually prefers front carries, so I got myself a toddler size Babies Beyond Borders buckle carrier (I have the half buckle, b/c I like the Mei Tai straps with the buckle belt). I LOOOOOOVE it! She feels almost weightless when I wear her on my front, b/c their support belt is so very supportive!