OK, all you woodworkers out there, 'fess up!

OK, all you Obi-Wan Kenobis, you're my only hope.

I have this silly molding that I'm putting at the top of my newly-refaced wall cabinets. If you go here, it's #M2. I cannot for the life of me figure out how to do these fucking miter cuts to do the inside and outside corners! Because I have to hold the damn thing either upside down or on its side (I'm using a good old fashioned miter box and hand saw), I'm completely discombobulated.

If someone can either direct me to a good site that might show me how to do THIS kind of molding (all the sites I've found just talk about the flat crown molding), or explain it so an idiot can understand, you would have my undying gratitude.