How to omit repeated authors with et al.,

I have ENDNOTE X3 and I wanted to make a specific style for the writing of my thesis. The problem it is that I didn’t find how to put the following style: (Smith et al.,1990, 2000) instead of (Smith et al., 1990; Smith et al., 2000).  I use the author date style
Thank you for your help

Open the style for editing.

Go to Citations>Author Name.

Under “Consecutive Citations by the Same Author”, check the box “Omit repeated authors…”

This way is  available only when it is about the same author (Smith, 1990), but when it is about a work of several authors (Smith and al., 1990) it is not possible. Because in this case Endnote X3 doesn’t take into account of the repetition (Smith and al., 1990; Smith and al., 2000). 

Thank you for your help