Alright then...
A boot code of "ssid=wifi_network" would satisfy what I'm after.
Nuh uh. That's the kind of thing that can (make that SHOULD) be set to start automatically when you boot from bootlocal.sh or what have you. An extension like wifiroamd would allow you to manage your connections as you desire, but it shouldn't be part of the base. If you start adding in such "features" then you may as well include drivers, wpa_supplicant, and everything else required to correctly/safely use wifi out of the box and all of a sudden it's no longer a modular distro.
When I was using TinyCore on my Aspire One and roaming a lot (and I mean a lot), I set up various scripts based on if or where I wanted to connect. I understand you want more ease of use, but is it really so difficult to set up something so you scan to see what's available and then connect to what you want, especially at hot spots like you want to which tend to not use WEP, WPA, or anything else?