How can I use a comma in a string argument to a rake task?

I have the following Rakefile:

task :test_commas, :arg1 do |t, args|
  puts args[:arg1]
end

And want to call it with a single string argument containing commas. Here's what I get:

%rake 'test_commas[foo, bar]'
foo

%rake 'test_commas["foo, bar"]'
"foo

%rake "test_commas['foo, bar']"
'foo

%rake "test_commas['foo,bar']"
'foo

%rake "test_commas[foo\,bar]"
foo\

I'm currently using the workaround proposed in this pull request to rake, but is there a way to accomplish this without patching rake?