Originally Posted by bootney
I was wondering if I could Vorlauf/Lauter/Boil enough wort to increase the grist to the desired rest temp?
Any portion of the mash you heat past ~170 degrees is going to have its enzymes destroyed. The enzymes are soluble and mostly exist in the liquid portion, so decoction boils are as thick as possible: you want to maximize the amount of grain boiled for gelatinization, but minimize the amount of liquid boiled to keep the enzymes intact.
Thus, I would worry about destroying too much of the enzymatic power with this method.