RRAS with VPN...creating DNS record with wrong IP address

Hello folks. I'm having a problem with the IP address that DNS is
publishing when using a PPTP logon vpn setup. The site with the
server uses a 10.31.1.x network and the site that is creating the PPTP
tunnel has LAN addresses in the 10.31.5.x range. When the user logs
in, there is a VPN connection setup that connects before logon by
checking the "dial this connection first" box which authenticates,
connects, and then logs the user onto the domain. After this, the DNS
record creates an address from their remote LAN IP (10.31.5.x) instead
of the tunnel address which is 10.31.1.x. I have the option to
"update DNS with this connection" set but instead it still updates the
DNS record with the remote address of 10.31.5.x. How do I get DNS to
use the tunnel address in the 10.31.1.x range? Thanks.