Clear values for multiple params and objects

Hi Andrew, great plugin!

Is there a way to clear referenced geometry in multiple params?
i.e. I've selected some params with the 'Select Object' component, is there a way to use these references with param.PersistentData.Clear() ?

I've found http://www.grasshopper3d.com/forum/topics/unable-to-clear-persisten... but am unsure how to implement it!