In WDS, you still have different IP numbers for the two access points (on the local network), right? I was going to recommend using ping -R, but I keep getting an error message when I try that. 🙁
The logic would be that you have an IP address for the router that is connected to the ISP (cablemodem, whatever), and an IP address for the WDS. If you ping the former, you will obviously always get the IP address for the former in the route. But if you ping it while you're connected to the WDS, you'll get both IP addresses in your route.
Of course that would all be nice if ping -R worked.... 😱