In my wanderings around the 'Net today, I ran across this product, which doesn't appear to have been mentioned on FT previously:
http://www.nadachair.com/slouchbuster.html. In addition to the Slouchbuster, there are S'portbacker and Backup devices, but the Slouchbuster appears to be designed for travel.
Anyone tried one? My sister's headed on an overnight flight to Ireland in a couple of weeks, and I was thinking of buying her one, but my instincts say it's probably a waste of money.