I'm new to C::B so please bear with me if this has been covered. I didn't find it when I searched the forums.
There is a very easy way to do "launch the associated application" feature for Mac version of C::B - use /usr/bin/open ! This makes LaunchServices do all the work. In current released version of C::B, you have to set this up as "Launch an external program" set to "/usr/bin/open", but it sure would be nice (any devs listening?) if a future version of C::B Mac could do this internally (in other words, implement "launch the associated application" as equivalent to "Launch an external program: /usr/bin/open").
With this setting, I can now easily launch Property List Editor for my Info.plist from within C::B. In fact, /usr/bin/open seems to be the only way to do so - setting the external program to Property List Editor doesn't work.