Case insensitive primary keys

[Jeff Schnitzer]

I have a primary key which is a string (user's name), and I would like
it to be case-insensitive.  That is, if there is already a "bob" entity,
trying to create a "Bob" entity should throw a DuplicateKeyException.
Is there a way I can do this with Orion?
 
I vaguely recall reading something in the documentation about this, but
now I can't seem to find it.  I'm starting to think that I imagined it.
 
Thanks,
Jeff