Joe I don't use actual Sugar in anything. Rhubarb I cook in apple juice (out of the litre box) very slowly, below simmer. I don't put sugar in custard either though for rhubarb I usually make tapioca (not tinned) and plop in a helping of the rhubarb. The sweetness of the apple juice does for the rhubarb and the tapioca.
I'll try the pineapple though.