Well, I found the answer, and for the sake of documentation (since this is incredibly poorly documented), I'll jot down the important bits.
First, setting the service to 'all' for international shipping on USPS will give a list of every service with the rate and name (that was the sekret part I couldn't figure out). Here is a Dumper of the array that is returned from a sample query:
To request a specific quote, you use the corresponding name from this object in the service=>'' attribute.
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