Database stored procedure send message to client - how to catch it?

Question

i use Sybase database. in this database is procedure, which have many inputs but no readable output. procedure after commit only send msgbox to client.

   Myprocedure(
  in a_ID                  IDINT,
  in a_OPERACE             NAZEVSTR,
  in a_UZIVATEL            JMENOSTR,
  in a_DATUM               DATUMTS_NU,
  in a_PARAM1              VALUESTR,
  in a_PARAM2              VALUESTR,
  in a_PARAM3              VALUESTR,
  in a_KOMENTAR            KOMENTARTXT
) returns void

and

perform admin_eng.ENG_ShowMessage( ...

i cannot change this procedure, because i dont have acces to it :-D

on other side, i have VB.NET aplication, with this aplication i call this procedure, and this procedure return me classics windows messagebox with result. i want catch this messagebox, Suppress this messagebox, and save result to variable.

        Try
            Dim cn As New System.Data.Odbc.OdbcConnection()
            cn.ConnectionString = "DRIVER={Adaptive Server Anywhere 9.0};ENG=ASA9;DBN=ASWINFO;Uid=" & dbuzivatel & ";Pwd=" & dbuzivatelheslo & ";Links=tcpip(Host=mydb.cz);"
            cn.Open()
            Dim cmd As New System.Data.Odbc.OdbcCommand()
            AddHandler cn.InfoMessage, AddressOf cn_InfoMessage
            cmd.CommandType = CommandType.Text
            cmd.Connection = cn


            cmd.CommandText = "call Myprocedure(
  a_ID = '" & id & "',
  a_OPERACE = '" & nazevbk & "',
  a_UZIVATEL = '" & uzivatel & "',
  a_DATUM = '" & datum & "',
  a_PARAM1 = '',
  a_PARAM2 = '',
  a_PARAM3 = '')
"

            cmd.ExecuteNonQuery()

            cn.Close() : cn.Dispose()
        Catch odbcex As System.Data.Odbc.OdbcException
            Dim err As System.Data.Odbc.OdbcError
            For Each err In odbcex.Errors
                MessageBox.Show(err.Message)
            Next

        End Try

any ideas how to catch this infomessage? try/catch work only on error messages, my handler for infomessage dont catch this event. i dont know how to ?-/