Maybe you can take a look at Nathanmx's addon.
I've no need to move the Capturebar myself so I can't say if it's working as advertised,
but his addons are generally good quality addons.
Wish I'd found that last night. Ironically, an hour after making my initial post saying "I'll never do this" I figured out what the problem was and fixed it. It turns out I had missed a function in the deep sea of the FrameXML directory. So, the CaptureBar is working beautifully. Going to add the CastBar tommorow and do a big release.