Set session cookies in test mode using selenium hd

I am trying to do part of testing using selenium hd. I currently have the following code:

    browser.goTo("http://localhost:3333/")
    browser.$("#email").text("michele@sample.com")
    browser.$("#password").text("secret")
    browser.$("#loginbutton").click()
    browser.goTo("http://localhost:3333/michele")

But I would like to be able to set a session cookie instead of doing this for each test.

I tried to do something like this

    browser.webDriver.manage().addCookie( new Cookie("PLAY_SESSION",
      "1dd6811c9df64e03a892f55f57dd0f1190656d88-email%3Amichele%40sample.com") )

but it doesn’t work, because I get an exception from the null pointer when I try to extract a cookie using        browser.getCookie("PLAY_SESSION").getValue()must contain("michele@sample.com")

Any help is much appreciated!