trigger a recompute on scene units change

After looking into converting values in grasshopper into scene units I found several good methods here on the forum. One was to use a component within caterpillar and another was using a custom c# component with:

A = doc.GetUnitSystemName(true, true, true, true);

Both work great with one flaw - they require a manual recompute when scene units are changed in rhino. Is there a simple way to trigger a component to recompute when a user changes scene units?

There's a discussion here on recomputing on layer events and I'm hoping this is a more simple thing to solve. Thanks in advance for your help.    

Yan