Yes, you can drill there, but only in the outmost edge of each of the four pod/feet things. The rubbery bits can be pried out with a knife/screwdriver first, and then it is safe to drill only outside of the "curved" edges of the router body.

If you want better access, open it up. Scary the first time, but here's how:

The blue/purple front detaches from the dark main body of the router. There are no screws (unless yours is old enough to have them under those rubber pads you removed above). Instead, just firmly grab one of the two back "feet" in one hand, the corresponding front "foot" from the same side of the router in the other hand, and pull hard/quickly. The front will snap apart from the main body, revealing the innards.

It helps to slice through the "do not tamper" sticker beforehand.

Looks like about 1/4" max space for drilling, on my v1.1 WRT54GL.

Cheers
Mark