Here is something that took way to long to find and, as far as I know, is not in the wlan-ng documentation. The sad part about this is that it's friggin easy you'll be slapping your head.
in /etc/wlan there is a file called wlan.conf. In this file you can specify your SSID or leave it "" for any that it finds. If you specify your SSID you need a wlancfg-SSID file configured for that SSID.
Configure a wlancfg-SSID for each SSID you have and then change wlan.conf with this information:
WLAN_SCAN=y
SSID_wlan0="ssid1 'ssid2' ssid3 ''"
Make sure you end with '' so it will connect to any wireless access point.
Multiple ssid's with wlan-ng
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