There is a CE report document in the files section containing the schematics and PCB layouts of the wl500gx device.
http://files.wl500g.info/asus/wl500gx/document/ * http://files.wl500g.info/asus/wl500g%20deluxe/document/
On page 10 you'll find that TDI/TDO/TMS/TCK are connected to resistor network RN21 and resistor R77, respectively.
Now go to page 23 and search for RN21. It's left of the processor chip. I haven't tried it but I'm curious if it works.
At least, EJTAG DeBrick Utility has some support for BCM5365 from version 4.4 on. http://www.dd-wrt.com/wiki/index.php..._WL500g_Deluxe
Good luck!
fritz