For Legacy Google Analytics (ga.js):
Check out this page on Google's Developer's Network.
You can set these values manually by adding values into the _gaq array that Google creates on page load.
For Universal Analytics (analytics.js):
You can simply map variables using the Campaign tab in the Mapping Toolbox within the GUA tag.
Your specific use case:
The difficult part will be parsing the URL to get these values. Because of the redirect, there is a good change the Google Analytics tag will not fire. As soon as the redirect begins the tracking calls will be cancelled. The best chance of tracking these will be on the following page where we get redirected to.
So on the landing page you can use something like this:
var str = decodeURIComponent(b['dom.url'].split('goto='));
var qs = str.split('?');
var qs_var = qs.split('&');
I updated my answer below. For legacy GA, you'll likely need to do some updates on your side to forward the query parameters to the new landing page. Legacy GA doesn't actually have very good support for this kind of thing.
Google Universal Analytics handles this much easier.
Here is a post explaining how to transition from legacy to GUA if you're interested.