Struggling with dimension lines
 

I trying to create a stencil to draw dimension lines on my diagram. I'm able to draw the dimension line with the text label containing the length of the line. I've got the arrows on both ends. What I'm having trouble with is adding the guidelines that lead from the dimension lines to the drawing. Please see the attached screen grab.

The guideline should be a fixed distance from the object it is dimensioning, and should extend a fixed distance from the dimension line. The problem is, I can't find a way to make these distances fixed and yet still allow the group to be dynamic. I hope this is clear. I'm struggling almost as much explaining it as I am to drawing it.

Can anyone offer some guidance? Has anyone else done this already?

Thanks