Setting up an angled cut.

Ok, So lets say you want to face and contour both sides of a part, Then you want to create a feature like a through hole through one face that is not normal to front or back.

You throw a chunk-O-material in the mill and face side 1 and contour the outline.
Next you flip the part over and indicate two sides to get your X and Y and face side #2. So far so good.
Then you want to drill the angled hole. You set up the angle using a sin plate or tilting angle table, you indicate off the side that is still normal to find your X, but how do you find your Y? You can't indicate off the corner because it may have burs or you may have chamfered it.

I'm stuck figuring out a good way of doing this. Can any of you pro's help out?

Thanks
Marc