The documentation you found indicates that the controller must be plugged directly into the wall. That may be excellent guidance, but I would suspect that it is written that way to keep things simple. There is no reason you couldn't plug it into an extension cord of reasonable quality. I would not plug it into a power strip of any kind since that could have electronics inside it that could cause issues.
The other choice is to plug the controller into the wall and use a longer USB cable (for CM15A). I was using a standard USB cable with a standard USB extension cable for testing and never had issues. In that case, the total cable length was on the order of 12' long. The USB spec indicates that a USB 1.1 device can have a cable length of up to 5m (~16.4 ft) with devices operating at full speed (
http://en.wikipedia.org/wiki/USB). I don't know what spec the CM15A falls under, but I suspect it's full speed so you should be able to get a pretty long cable or extensions and make it work. If it was actually a low speed device, you still have a maximum of 3m cable length (9.8 ft). If that didn't work, you could also use one of a couple other choices.
1) USB repeater
2) USB -> Cat5 adapter
Both of these have threads on the forum that should provide help.
Alternately, you might be able to set everything up within a CM15A such that you don't need a PC at all. If that were the case, you can simply plug the controller into any outlet once programmed and effectively never think about it again.