The following two links are about hypothermia kits and how to use them for adventure kayaking type events, all based around a PFD. The hypo kit is a good start and does not rely on a fire for heating in the immmediate aftermath; rather heat retention and small heat addition. Take a look.
Everglades challange, emergency action
http://www.watertribe.com/Magazine/Y2002/M12/SteveIsaacWhenGodsPlay.aspxHypothermia kit
http://www.watertribe.com/Magazine/Y2002/M12/SteveIsaacMakeAHypothermiaKit.aspxBill