Hey solid7,
The method that you suggested is similar to just creating a CATPart from a product but allows you to choose what parts you would like to bring over to the new part, which is really handy.
I continued looking in the help files for some idea on how to create a section cut a specific location and found it!
When being in the sectioning definition dialogue box, select the position tab and click on the "geometrical target" icon, then select a plane or face that you want the section cut to be located.
ryengnut