[Nyororin]

In my opinion, it would just be Jasutin. (ジャスティン), or if you would prefer - Jasuten (ジャステン).

Both of those would be significantly closer that "Jusan" - which as said in Japanese doesn`t resemble "Justin" at all. The fact is, you can`t say "Justin" in Japanese exactly as you say it in English... And you`re getting further away from it`s normal pronunciation by trying to hook it to "Jusan".