The routesplit tool fails to make routes permanent on Snow Leopard and later versions of OSX.  To work around the issue edit the following file as such:

/Library/LaunchDaemons/net.routes.static.plist...
<key>ServiceDescription</key>
<string>Install static routes</string>
<key>WatchPaths</key><array>
 <string>/Library/Preferences/SystemConfiguration
</string>
</array>
...