I'm wondering what the best method is to bring hardwood up to a bullnose that is on a diagonal...

Chris

With pretty much any bullnose situation where my flooring running perpendicular to it , I make sure my under layment is cut back a couple of inches from the bullnose so that I can put some flooring adhesive in there. And then run my boards up to it ,staple where possible and the glue will do the rest.

A fancier way to do it is to put a piece of spline into the bullnose (which has a groove on the back side)cut your diagonal end pieces and then cut a groove into the end , then the end pieces will lock into the tongue that you slipped into the bullnose . You can still use some glue.