Ok, for what it's worth, it IS in the STK-500 user's guide under ISP Programming.
What I was looking for was "socket selection" which is right above that, and tells you essentially nothing about selecting which socket to use, almost as if it should have been a link to the part in the ISP programming section that does.
Anyway, in case someone else needs to find out how to pick which socket for which chip on the STK-500
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Feel the power of the dark side! Atmel AVR
Feel the power of the dark side! Atmel AVR