Dealing with negative dimensions

I am currently working on a project where I am manipulating solidworks via VBA in MS Excel.  I have a user input form on a worksheet, and based on the dimensions entered, the solidworks model changes and performs some calculations.  The problem is I need the user to be able to enter negative values in the input form and have the model respond correctly.  In a simplified form here is what I need.

What am I going to do about this?  I thought about abandoning the use of dimensions all together and just programatically moving the points to the correct coordinates but 1) I don't know how to do that and 2)  I'm afrriad they will start moving if they are not "held" there by anything.

Also, I know there is a 'Reverse Direction' button whenever you let go of the dimension it forgets what position it was in originally.  I wish is would remember it's original position.  Then I could check to see if the dimension is in a reversed state and act accordingly based on the sign of the input value.  However, b/c it resets itself, it's pretty much useless.

If anyone else has idea please share.  I'm running out quickly!

Thanks

Kyle

SolidworksApi macros