"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?

Try to use automator. It's simple: create a new service with preferences (what items in which program to open). That's all - on right click menu there will be a new rule - "open in ...".

You could just drag the file onto the App icon in the Dock… [which is very difficult to take a screenshot of…]

[after comments…]
Alternatively, you could…

• drag the file onto the app switcher - the one you bring up by pressing Cmd ⌘ Tab ⇥

or

• use DragThing which has been a kind of substitute Dock since long before the Dock existed.