With BIAG, do you just lift the bag and start boiling? If so, then you could actually do mash/FWH at once?
Put hops down, then bag, add water, let mash/soak. Lift bag, hops are now FWH'ing up to the boil.
The disadvantage of mash hops being they get tossed with grains, but perhaps with BIAG not entirely lost?