Hi Deerman,
The EXBAC crossover optimizations in our 340 SE center help compensate for close proximity placement of the speaker. This combined with an 80Hz crossover setting in your receiver (which greatly reduces the bass response of the speaker, thereby reducing the amount of air moving in and out of the port) should allow for placement as close as 6” inches to the wall behind it without compromising performance.
With that in mind, I would recommend some type of shelf mounting system. Perhaps a small shelf to hold the speaker or something like this bracket:
http://www.pinpoint-mktg.com/bt15.html
Hope this helps!