The only forecastle extension I can recall off-hand is that which was applied to the 'Flower' class corvettes of WWII. whereby the foc'sle deck and side plating were extended aft from a point forward of the bridge to a point abreast the funnel and, in some cases, even further aft. I am not sure how much weight was added but crew accomodation and seakeeping were much improved. It made them look much better and, quite possibly, increased hull strength.
Of course, corvettes aren't destroyers but maybe it's something you can work on.