Here's an option, that will only work with real tongue and groove. (That is, that you can T two pieces and have the t&g match) I'd lay out a few pieces and see if it will work for you or not, but it's probably the easiest install.
At D, I've got one piece which is the stair nose (assuming we're at the top of the stairs.) If it's the bottom, then don't worry so much. You can simply rip the end piece. and proceed according to The Evil Greebo's answer