Suggestions for wall mounting 170s?

I bought 5 170s a year ago. I recently rearranged the things in my living room and having a hard time wall-mounting the 170s. The right side of my listening position opens to the dining area (no place to mount the RS on the side wall). My listening position is up against the rear wall. I am planning to mount them on the rear wall, but facing each other. Ceiling mount is not an option. I thought of building a shelf (12"x12") with a single shelf bracket, but I don't know how sturdy it would be. Any suggestions?

Thanks!

Maybe someone makes an articulating mount that can swivel 90 degrees, so you can mount on the back wall then swivel them inwards towards each other. From what you're describing, you may need only one of these on the back wall & the other mounted normally on the side wall. Omnimount may have some in their Pro series. I tried looking, but their site's kinda confusing.

Not sure if this will work, but will take you to their Pro line:

http://www.omnimountpro.com/products.asp?p=56