"Open With" ...running application option?

This may have been asked before but I couldn't find any reference to it.

So Control-Click on a file brings up the context menu with "Open", "Open With.." and a number of other options. I often want to open a text based file in something other than the default application – for example, opening an mxml (Flex) file in BBEdit. The default application for that is Flash Builder and I don't want to change the default.

Is there some kind of extension or service I can add to have an "Open with Running Application...(list of open applications)"?

Or if not that, a way a user (me!) can register an app to open certain file types, so for example, BBEdit is listed as an option for mxml but is not the default?