Simple way to get a well formatted request:
* Go to the history tab (http://www.rdio.com/people/username/history/) and pull up the inspector
* Scroll down once or twice and go to the network tab
* Find the `getHistoryForUser` request and right-click it, select "copy as cURL"
* Paste into your editor and change the "start" param to 0 and the "count" param to 99999
* Make the cURL request. Boom, no rate limiting. I got 3.5mb of history (though it seems to only go back 1 year.
I did manage to get the past year though, via a comment below.