Read what Mr.Dempsey said:
Porsche Boxster Brake Bleeding - 986 / 987 (1997-08) - Pelican Parts Technical Article
It may be advantageous to put the rear as high as safely possible .
Without a pressure bleed system ,I doubt you will succeed.
If you are a visual learner, this may get you started?
https://www.youtube.com/watch?v=mwvJxjqMYCQ
If you have problems with air in the ABS or other ABS issues, that is a different remedy.