The same way you balance any other propeller. Carefully, using a setup that induces as little friction as possible, allowing it to rotate on an axis that is as straight as possible.
Like this:
http://www2.towerhobbies.com/cgi-bin...&I=LXHY61&P=ML
http://manuals.hobbico.com/top/topq5700-manual.pdf
Do you have a specific problem, or are you asking for directions to balance any propeller?