Removing double quotes from JSON.Simple JSON parser/writer for keys

I would like to remove double-quotes from keys of JSONObjects (JSON.Simple) when converting the object to a String.

For example, I have the following JSONObject:

JSONObject object = new JSONObject();
object.put("foo", "bar");
System.out.println(object.toJSONString());

Which outputs:

{"foo":"bar"}

And I would like to remove the double quotes from the key object, foo:

{foo:"bar"}

Although this would not become valid JSON, how can I accomplish this? Should I be using regex for this case?