I'm not sure this is a sound argument. Rather, I just want to see what "sticks" and what doesn't.
1. Whatever is possible is necessarily possible. (Premise, S5)
2. Necessarily, the universe is intelligible. (Premise)
3. Possibly, the universe's intelligibility is known by a person. (Premise)
4. Necessarily, the universe's intelligibility is possibly known by a person. (From 1 and 3)
5. Whatever is necessarily possible is possible in all possible worlds. (Definition)
6. Necessarily, a person possibly exists in all possible worlds. (From 4 and 5)
7. No contingent person exists in all possible worlds. (Definition)
8. Therefore, a necessary person exists. (From 6 and 7)
I think the weakest premise of the argument is (6). It is susceptible to the charge of equivocation, where "person" is used to describe any person in the preceding premises, but refers to a single person in (6). Nevertheless, I think there's some promise with this argument. It just needs some tuning up.