in rubygem package provider

quick hack.rb

def with_gem_sources(*sources)
   sources.compact!
   original_sources = Gem.sources
   # Gem.sources = sources unless sources.empty?
   unless sources.empty?
     if Gem.respond_to?(:sources=)
       Gem.sources = sources
     else
       Gem.instance_variable_set(:@sources, sources)
     end
   end
   yield
ensure
   if Gem.respond_to?(:sources=)
     Gem.sources = sources
   else
     Gem.instance_variable_set(:@sources, sources)
  end
end

rubygems 1.3.7.rb

# this method doesn't exist in v 1.2.0 of the Gem module, but does in 1.3.7 (haven't checked what version it was introduced yet)

def self.sources=(new_sources)
  @sources = new_sources
end