There's a thread in the macosxhints forums discussing a way of opening a document in an X11 application by simply double-clicking on it in the Finder. The following is taken from the forum, as written by the author of the solution:
Problem solved!The solution is a program called XL. XL can open, by default, documents with .ps, .xpm, .tex, and .lyx extensions, but you can (taken from the info on the site) "map any document type to any application by simply double-clicking on the XL icon and selecting preferences from the XL menu."
Well here is a solution to the problem, maybe not the best one but it WORKS and you can double-click documents associated with an X11 application and have them open!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020927044738228