The following method isn;t exactly what you are looking for, but may work for you. It doesn't get the value from the property boxes, but from its instances in the part sketches.
1) Create the sketch
2) Double-Click on the Dimension that you want to be the referenced/controlling dimension.
3) In the little pull-down menu next to the value, select 'Link value'.
4) This brings up a window where you can name the variable, and it will assign it the value from the sketch.
Now note at the top of the feature manage there is now an 'Equations' Folder and it contains the dimension value from the sketch and its description.
You can now link other dimensions to that same variable by double clicking on them and 'linking' them to that value.
When you change any of the dimensions that reference this variable and it will update all of the dimensions.
Beware: as intended, changing one will change them all
Hope this helps,
Lou