For the time being, you can’t do this automatically, although it is a common request and I am sure the developers are trying to implement this in a future version of Endnote.
In the meantime, if you are working in CWYW, select the author name and drag it out of the field to in front of the parenthesis, and then edit citation to hide the author (right click in field, edit citation, or choose the edit citation tool from the endnote toolbar). If working with CWYW off, you just need to drag the name out, which will effectively eliminate the author from the formatted citation.