gcoffee, the trick is in how the CC3000 works. When you initially get the Spark and register it, you created a connection profile on the CC3000. Several profiles can be stored in the CC3000 and I believe you can create a profile within the code. As for scanning for available wifi, Dave (Spark Team) posted this on one of the topics:
If a stored profile matching an active wifi is found, the Spark will attempt to connect to it when you turn on the wifi. You could, in theory, keep wifi credentials for known SSIDs and manually connect to each when you detect them. I am guessing on the manual connection part and @Dave may know more. Also @timb could help you. I just haven't dug into that part of the code yet! 