Mark is absolutely right! I think I got mistaken here.
The rate only affects the speed of exit opening, I got confused and mixed it up with the jetway speed.
Sorry for that, I have checked and every question regarding the jetway speed leads to the conclusion that it cannot be changed in FSX. However some people speed up the sim rate, unrealistic but it all depends on what you find acceptable.

Best Regards,
Marc

P.S. I just found the page were I had read about jetway speed but they may have made the same mistake, trying it out would quickly show you whether it works or not.
http://www.ehow.com/how_12224699_make-downloaded-plane-use-jetway-fsx.html

Best Regards,
Marc