Yes, I had considered this firstly, but in some post i read that username generator cannot be used for all the attributes. It can only be used for deriving accountid.
Please find the details for the same in below link.Is this correct? Can you please confirm?
usernameGenerator Transform - IdentityNow (IDN) / Discussion and Questions - SailPoint Developer Community Forum
This solution may not work for me as again i have to do a pattern check.