You may need to write a little custom code if I am understanding what you are asking... I don't thing that out of the box workflow supports custom headers. Something like this:
var request = restOperation.createRequest(inParamtersValues, content);
//set the request content type
request.contentType = "application/json";
var response = request.execute();
In the example above you'd pass in "token" and replace "Your-Custom-Token" with whatever you are expecting.
Were you able to get this working?
Did this work for you? If so can you please mark my response as the answer? Thanks!