Outlook Digital certificate without contacts

So I need a solution to have users be able to send encrypted emails to PersonA, but personA cannot be in the GAL.  I guess users can add them to their contacts but we have thousands of users that need this.

I was wondering if there was a way to impor the public cert to the users Certificate store and outlook would be able to pick it up?

Any ideas. I thought about creating a contact on the GAL and hidding it, but once you select to hide it then users can not see it, so they wont be able to get the cert that way either.

Thanks.