You could either use the method with ~/.MacOSX/environment.plist (see for example
http://www.astro.washington.edu/users/rowen/AquaEnvVar.html) or you can put into your init file something like:
(setenv "PATH" (concat "/some/directory/with/R_and_matlab" path-separator (getenv "PATH")))
(and also for Eacs-only EXECPATH).
A third option is to launch Cocoa Emacs from a shell script or AppleScript file which internally sets PATH correctly like in this example:
env PATH="/some/directory/with/R_and_matlab:$PATH" open /Applications/Cocoa\ Emacs
--
Greetings
Pete
Who the fsck is "General Failure," and why is he reading my disk?