Can't you add it to the Calibre Info.plist? Surely every way of launching Calibre would then see it or will that break code signing? Ala this example:
Code:
<key>LSEnvironment</key>
<dict>
<key>PATH</key>
<string>/Users/flori/.rvm/gems/ruby-1.9.3-p362/bin:/Users/flori/.rvm/gems/ruby-1.9.3-p362@global/bin:/Users/flori/.rvm/rubies/ruby-1.9.3-p326/bin:/Users/flori/.rvm/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:</string>
</dict>