Hi there,
You can use the relation. A simple way is to select the base member and then right click on on it and select "Copy Selected Members." From there, click on the new parent you would like to add it to and then right click and select "Paste Relationships (Add)." This will add the base account to the new respective parent and every instance that respective parent member is shared throughout the hierarchies.
As Manasa stated, keep in mind that any changes to the base member will be reflected in all shared relationships.
Thanks,
Adam