AFAIK we can only copy/paste (ctrl+c / ctrl+v) in 2d. Don't know why can't we use regular copy/mirror/multiply module elements.
You can do those three operations to a module, but you can't do it to a sub-element. This probably has a lot to do with the current data structure for the management & handling of modules. From recent inquiries it seems that modules are treated as a special external reference not to be modified within the host without embedding them first.
You could always pull a copy of the module to one side of your drawing, embed the contents and delete the unwanted elements. The other method would be to "Edit the module in a separate ARCHICAD" and copy the elements from there to the host file. Neither are as quick as what you are requesting though. For now I guess it depends whether it is quicker just to draw what you need or extract the parts from the module.
P.S. Depending on your subscription status you may be able to gain access to the following document which may give you more insight to how GS expect modules to be used... Graphisoft Workflow Guide - Hotlink Management