Excuse the late reply, but I struck a similar predicament myself and thought I'd offer advice.
In short, if you intend on using $location.search you cannot avoid the URL being encoded.
If you take a look at the Angular source, location.js specifically, you'll notice that the functions return composed URLs (i.e. LocationHtml5Url) all rely on another function call named toKeyValue, which will encode all key-value pairs whenever they are set.
Furthermore, in the example use case you've provided, you don't need the equals inside your key. When $location.search is called with two parameters, they are treated as a key-value pair by Angular.
If you need to make use of the location URL after it has been encoded, you could always call decodeURIComponent.