One way of stretching your fuel is to use a pot cosy - an insulating jacket and lid made from Thermawrap (
this stuff). Backpackinglight sell small quantities suitable for a couple of pans at less than a full roll.
Bring the pasta/rice to the boil, then take the pan off the stove and put it in the cosy instead of simmering. You can then use the stove for the sauce, or just snuff it and save fuel.
Trangia pans are a more awkward shape for making a cosy for than a basic cylindrical pan, but you should be able to come up with something reasonable.