We do not currently have the ability to link two design variables together except those that are explicitely defined on the Concepts tab.
For example, in the corrugated family, one of the options on the Concepts tab is the link flange and web thicknesses. This option causes the optimized design to have a constant thickness between the top flange, web, and crown thicknesses.
However, if the linkage is not already explicitly spelled out on that tab, we have no way to link variables together.