gistfile1.txt

[andre ~/sw/gems/bundler-testcases/i850]$ cat Gemfile
gem "rack"


[andre ~/sw/gems/bundler-testcases/i850]$ dbundle install
Using rack (1.2.1) 
Using bundler (1.0.5) 
Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.


[andre ~/sw/gems/bundler-testcases/i850]$ cat test.rb
require 'rubygems'
require 'bundler/setup'
puts "With env: #{ENV['BUNDLE_GEMFILE']}"
Bundler.with_clean_env do
  puts "With clean: #{ENV['BUNDLE_GEMFILE']}"
end


[andre ~/sw/gems/bundler-testcases/i850]$ echo $BUNDLE_GEMFILE


[andre ~/sw/gems/bundler-testcases/i850]$ ruby test.rb
With env: /Users/andre/sw/gems/bundler-testcases/i850/Gemfile
With clean: 

Sorry, I don't understand your question. What do you want to be able to do?

From an application, load code which may itself have distinct dependencies described in separate Gemfiles. Plugins are a canonical example - it would be nice to be able to distribute plugins with 'bundle install --deployment' dependencies which can be loaded from the parent application without requiring all possible plugin dependencies to be added to the app Gemfile a priori.

No, unfortunately that's not possible. The ruby interpreter is only able to load a single set of libraries, which is why Bundler has to resolve the entire dependency graph before the interpreter even starts.