I have experienced the same issue and decided to look into it. Here's what I found to help the situation. I'm ordering mine today.
http://cgi.ebay.com/ebaymotors/TRD-B...item4153be6b7d
This item should help by supporting your neck and allowing your head lay back some. I have noticed on longer trips that I wish I had a neck support just for this reason. Now I will.