Route some ips over VPN ppp0 mac os x interface via http://archives.aidanfindlater.com/blog/2010/02/03/use-vpn-for-specific-sites-on-mac-os-x/

ip-up

#!/bin/bash
#
# Script which handles the routing issues as necessary for pppd.
# When the ppp link comes up, this script is called with the following
# parameters:
#       $1      the interface name used by pppd (e.g. ppp3)
#       $2      the codey device name
#       $3      the codey device speed
#       $4      the local IP address for the interface
#       $5      the remote IP address
#       $6      the parameter specified by the 'ipparam' option to pppd
#
log=/Users/David/ppp.log
$stamp=$(date)
echo $stamp >> $log
echo $1 > $log
## Routing setup for VPN

# Array of hosts to route for
# These are the domain names and IP addresses that will be accessed through the VPN
VPN_ROUTE_FOR_HOSTS=(172.19.200.15 10.3.0.9)

# Make sure we're in the VPN
if [[ $1 == "ppp0" ]] ; then
    echo Proceeding >> $log
    # Add the routes
    for k in ${VPN_ROUTE_FOR_HOSTS[@]} ; do
        echo Working on $k >> $log
        for l in $(dig +short $k) ; do
                echo Adding $l >> $log
                /sbin/route add -host $l -interface $1
        done
    done

fi