Read that tutorial again. If you combine them into a new, upper level component and also set a gluing/cutting plane for this, you can handle the two together, insert them etc. from the component browser and explode them at the end (so there are two, opposite ones now on the opposite faces - do not explode these). Here is an example model. http://sketchup.google.com/3dwarehouse/details?mid=a7960f12cf33423c9c6e1dd67923b5cd