I have one NAS device at home and I want to access it from office unfortunately default VPN client in MAC OSX doesn't have built in option to specify which traffic to go over current connection, it has only one checkbox which says "Send all traffic over VPN connection" but I don't want to send all traffic over my home router, it's slow and etc.
Probably good option is to use some other VPN clients like "Shimo" but there is other quick and simple solution.
Solution is pretty simple, because I'm using PPTP for VPN which is basically "pppd" program, I can create a script in "/etc/ppp/ip-up" with execution permissions, for example:

cd /etc/ppp
sudo touch ip-up
sudo chmod +x ip-up

And file content can be:

#!/bin/sh

if [ "${5:-}" = "192.168.89.255" ]
then
    /sbin/route add 192.168.88.0/24 $5
fi

IP address

192.168.89.255

is given by VPN server to me and it's same every time.
When the VPN link drops, those routes are automatically removed.
More examples for ip-up script can be found at
http://www.tldp.org/HOWTO/PPP-HOWTO/x1455.html and https://ppp.samba.org/pppd.html