I told a client I'm about 99.9901% sure this isn't possible, but figured I'd cover all bases:
Said client would like to IMPORT their legacy users into Foxycart: email, [password created on the fly], and their contact information. This would be a mass import via a script. If the above isn't doable, the client will have CSRs do this manually and send an email to each user alerting them of their new login information. I've posed my concerns about the logic of doing either of the above to the client, but still have to ask.
Thank you kindly for the help.