How do i set properties on request when using superagent for mocha tests

I'm running a mocha test for an Express api like so: My app is already started in the backbround

var request = require('superagent');

describe('Member Food Tests',function(){
    var domain = 'http://127.0.0.1:3000';
    var postEndpoint = '/api/members/v1/cmx/'+memberId+'/foods/';


    it('should post',function(done){
    //console.log(request);
    request
      .post(domain + postEndpoint)
      .set({'Cookie': ['aspxauth=YYYYYYYY', 'another=ANOTHER']})
      .send(fixtures.memFood1)

      .end(function(err,res){
        if(err){
          throw err;
        }

        done();
     })
});

In the above code, I'm able to set a cookie as shown above- the req.cookies get set by the cookie-parser module. But say i want to set another property on the request object - like req.market before the it hits the API. How can i do that. Is there a way to define some sort of middleware that traps the request, appends the property, and then forwards the request so that when the request comes to the endpoint, that property is available directly on the request. ( I can easily set it on the header by doing :

.set({'Cookie': ['aspxauth=YYYYYYYY', 'another=ANOTHER'],market:"US"}) 

but i need it directly on the request