as you may already know that this operation relies on netbios, which in fact is broadcast traffic. thus vpn client software will not encrypt and send the traffic via the ipsec vpn tunnel.
one way is to deploy a wins server, and configure the pix to push this settings.
e.g.
vpngroup myvpn address-pool vpnpool
vpngroup myvpn dns-server 10.1.1.100
vpngroup myvpn wins-server 10.1.1.100
vpngroup myvpn default-domain yourcompany.com
vpngroup myvpn split-tunnel 100
vpngroup myvpn idle-time 1800
vpngroup myvpn max-time 86400
vpngroup myvpn password ********
