I don't think you can use that operator with the ADO filter method, as it is performed on an existing recordset (not the table, query or SQL it's based on). The help file specifies
"Operator must be one of the following: <, >,<=, >=, <>, =, or Like"
One workaround, would probably be (re)opening the/a recordset with a new where clause (including a subquery), if you can't build a filter with
rs.filter = "field <> " & somevalue & " and field <> " & someothervalue & " and...