Thank you.  I will try it.

However.  I don't want to pass "nil" as the additional_param, I want  
to pass an object. Inside of my Ruby program, how do I find the object  
that I pass into the additional_param parameter?

To answer my own question, after looking at samples on the web that use RBBundleInit, it appears that the invocation I was missing is this:

require 'osx/cocoa'
OSX.init_for_bundle do |bundle, additional_param, consoleLog|
# bundle - The bundle being initialized. Presumably an NSBundle? Passed as second param to RBBundleInit
# additional_param - Whatever you passed to RBBundleInit in the third parameter # consoleLog - Used to pass NSLog messages to the console
  # something here...
Experimentally, I was able to determine that I can use a similar block with RBApplicationInit.  However, since I have no real need to get at command line arguments, and given that this mechanism was recommended here, I'll stick with this.