Thanks for the suggestion. We've had a chat here and decided that for the moment our UI is already quite large, so we'd prefer not to add additional controls that replicate a feature that could be achieved relatively easily using other means. In this case, you should be able to scale the geometry by selecting the source objects. Alternatively, you might be able to do something with Forest Effects. The attached Forest Effects file allows you to scale a subset of the geometry list. Set the range from the geometry list using GeomListStart and GeomListEnd. The geometry list counts from the top down starting at 0.
I hope that helps,