Create a unique Wordpress username with Userpro plugin and its facebook connect -- 4

I am using UserPro plugin to register new users. I want to use the Facebook connect feature. Problem It registers your username as your facebook username which is your email address. This unfortunately means your email address is on display in your profile url. I would like one of the following situations: I would like your wordpress username to be the first half of your email plus some sort of random number at the end of it so that you avoid duplicates. OR I would like your wordpress username to be a unique random mix of numbers or letters (to avoid duplicates). PLEASE: the most important thing is that all usernames are unique. I can tell you the exact file to change.