Using Auto-Dimensions for sketching (only when keyed in) does create driving dimensions. So, I looked at the IntelliSketch options for Auto-Dimensions, but that didn't seem to result in driving dimensions on the Box feature.
I am not an expert on Synchronous, so maybe someone else will know how to change that.
Don't believe you can as that goes against the direct edit philosophy of Synchronous. Idea is you only lock those dims that have to stay static through all edits becuase it is critical to design intent.