SSPR QA gates - how to force re-register if programatically registered?

I work in a university environment and I'm working on getting FIM 2010 R2 SSPR set up to allow students and employees to register for and reset their own passwords, replacing an existing 10+ year old system.  I've more or less identified how to pre-register accounts with PowerShell using the same data we currently use for first-time use of accounts.  Currently, first time users are asked for ID # (which they are provided ahead of time), last 4 digits of SSN and date of birth.  My challenge is that I'd like subsequent password resets to use a different set of questions (or at least potentially questions from a larger set than we pre-populated answers for).  Does anybody have thoughts on how this might be accomplished?  I'm open to reasonably secure alternative suggestions as well.