For the last few years there has been a useful quirk in the insert model dimensions command.  You could actually start the command and show all dimensions for a model or feature. Then while that command was still open you could delete the dimension that you wanted to keep and "X" out of the command. Then only that dimension would show up on the drawing.

Sadly, now that has been fixed in 2011 SP 2. You have to show all the dimensions for that feature, then delete all the dimensions except the one you want to keep. Technicall more accurate, but definately the long way around.