When my neighbor had a new install, the installer took off the outside wall a 'TV Box' and installed a new 'TV Box'. It is about 3 1/2 by 6 or 7 inches. I asked the installer what he was going to do with the old box and he gave it to me.
I would check local hardware or HomeDepot to see if they have something like this. (or look for an installer and see if he has any throwaways)
It has a large and small hole at the bottom/short end and would be ideal. I haven't put mine to use yet. (lazy)