You can just do it my regular US mail. But on the form that you mail him, the ex-boyfriend has to check a box and agree to "waive service".
If the ex-boyfriend doesn't waive service then you have to go out and hire a pro to service him. But then after he is serviced, he has to reimburse you for the service costs. So it is in his best interest to waive service.
I know this because I just got a part time job.