What alternative gelling agents can I use for jam and marmalade? Rather than using natural pectin from the fruit being used or added pectin I am looking for an alternative setting/gelling agent that will enable me to get more jam from my two principle ingredients (fruit and sugar). In other words, if I want to stretch my ingredients to create more volume, what else could I use to ensure it gels to the correct consistency while at the same time not losing its flavour?
Tapioca Jelly is interesting stuff: 


  A typical recipe for tapioca jelly can be made by washing 2 tablespoonfuls of tapioca, pouring a pint of water over it, and soaking for three hours. It is then placed over low heat and simmered until quite clear. If too thick, a little boiling water can be added. It can be sweetened with white sugar, flavored with coconut milk or a little wine, and eaten alone or with cream.


Of course, not all tapioca jelly recipes are yummy at first go, so you'll have to experiment.

Powdered tapioca starch is the starting material of choice, not the pearls or cubes etc.