Aligning text to always be on the outside of line

I know how to align text diagonally, but I'm having trouble aligning the text to be always on the outside, as the diagram shows: http://i38.tinyp开发者_C百科ic.com/rs4zlj.png The lines will always be positioned as a triangle.

What I get instead is, depending on the angle, text is inside or out (and upside down). Is there any math that can help me out here? I have the angle of every line, if that is helpful at all.