"Form New Sub-Assembly Here" including patterns/mirrors?

How can I form a new sub-assembly including patterns or mirrors? Using either the Ctrl+select in the FMT then right-click and select "Form New Sub-Assembly Here" OR Insert -> Component -> "Assembly from [Selected] Components"

I have a stairway with the steps in a linear pattern in my main assembly, and want to move them to their own sub-assembly.

Thank you,

Scott

SolidworksAssemblies