If you have a good understanding (or even if you don't, there are plenty of grain descriptions out there) of what specialty grains contribute as far as flavor, and you know about how much base malt grain or DME/LME it would take, be creative. I am constantly brewing stuff with "leftovers" , one project is in a bourbon barrel right now, and I used leftover carapils and crystal 60 with a bit of honey malt for a bourbon barrel ale. I use the Brewers Friend recipe creator right here, it will tell you all you need to know after you plug in the specifics.