I've already got one so no use to me, however I noticed that there is a rear seat conversion with fittings on ebay. starting at 99p!
I know these are rare so I bet the cost will shoot up but even so thought it was worth letting you GT6 boys and girls know about this in case you want to
try your luck at bidding for it......
http://cgi.ebay.co.uk/Triumph-GT6-Rear-Occasional-...