The easiest solution (if you have a webspace/server somewhere):

#!/bin/sh
echo "Content-type: text/plain"
echo ""
echo $REMOTE_ADDR
[download]

Just call this CGI and it will tell you your IP address (at least if running on Apache).

If you want to go at the router. I don't know this specific router, but many boxes support syslog. If you're able to run a syslogd and make it accept messages from the router (usually easy command line option), you always get the IP from the "connected" messages fresh on your hard disk.