This would require that you modify core, which I don't recommend since you'll potentially have to keep updating it release to release of DNN.

But if you desire:

Library\Components\Skins\ActionBase.vb

Look for this:

Private Sub DoAction(ByVal Command As ModuleAction)
            If Command.NewWindow Then
                Response.Write("<script>window.open('" & Command.Url & "','_blank')</script>")
            Else
                Response.Redirect(Command.Url, True)
            End If
        End Sub

From there it's as simple as using the params here:

http://www.javascript-coder.com/window-popup/javascript-window-open.phtml