How do I cause standalone X11 apps to use MacPorts X11?

[Kevin Reid]

When I run X11 applications built by MacPorts, they open in the X11 server “app” built by MacPorts (/Applications/MacPorts/X11.app). When I run separately distributed Mac-packaged X11 applications (MCEdit, Closure (the game)), it opens the “X11 is no longer included with OS X” dialog.

How do I get these applications to recognize MacPorts' X11?

I tried searching for existing advice and the most relevant-sounding thing I found was 
this:
http://superuser.com/questions/459273/x11-and-mountain-lion-how-to-use-macports-xorg-server
which suggested such mucking-about-with-system-files as "sudo ln -s /opt/X11 /usr/X11".

Is there a clean way to get these apps working?

-- 
Kevin Reid                                  <http://switchb.org/kpreid/>