IPSEC Dailup VPN without changing client DNS servers

Is it possible to create an IPSEC dailup VPN connection without changing the client DNS servers? The default options are to use System DNS or specify a DNS server but we need a solution which doesn't specify a DNS server at all so the clients will keep using their own DNS servers. Off course this is for a split-tunnel IPSEC VPN so DNS server on clients own network is reachable. Specifying the clients DNS server in the VPN configuration is not an option because the clients (and their DNS servers) are not known.