Hey Sherm. I have the LT contact in San Diego since I'm also putting in the request for San Diego IFS. Basically, your son would have to call the LT and say how he has reported to NASC and requests to do IFS in SD. The LT would agree to talk responsibility for him, etc.
Also, this is a no-cost TAD. Basically, he wont get reinbursed for travel expenses. But he'll still get paid base pay, BAH and BAS.
As a reminder, he'll have a butt-load of paperwork during the 1st wk or so after check in. He could also go to the IFS office inside the API building and speak personally with them. Good luck.