Setting arbitrary windows as frame's minibuffer

[Akio Burns]

I would like to set an arbitrary window as the frame's minibuffer so that I may 
position the minibuffer adjacent to the focused window when it is invoked 
rather that at the bottom of the frame.

After removing the validation in frame.c

          if (!MINI_WINDOW_P (XWINDOW (val)))
            error ("The `minibuffer' parameter does not specify a valid 
minibuffer window");

I tried setting the frame's minibuffer with

    (set-frame-parameter (selected-frame) 'minibuffer (selected-window))

This works for the first minibuffer invocation. Unfortunately, once the 
minibuffer quits/closes Emacs becomes stuck trying to resize the window and the 
minibuffer visually migrates back to the bottom of the frame.

Given that minibuffer window can be placed in a separate frame, it seems to me 
this should not be difficult. Am I missing something simple that would permit 
arbitrary minibuffer positioning?

—Akio