I know that all my extract batches from my LHBS came with instructions for EXTRACT kits, that had steeping grains, to add your grain, then bring up to temp. I only have 5 BIAB batches so far, but I am thinking it might not be a good idea.
With my limited knowledge, using that method for steeping grains is fine. But with pounds and pounds of grain, it might not be the best idea. Everything I have read is to bring it to your strike temp, add grain, cover, and let mash for you indicated time.
Although its kinda like a doing a protein rest, but you would quickly make it through the proper temp and would not be holding it.
Whats the reason for wanting to add then heat? To save time??