I'm not sure I understand. The school year has just begun, and he's currently a 3rd grader? But he already took the iLEAP, which is issued at the end of 3rd grade (in which case, that would be out-of-level testing)? But you're looking at skipping him two grades at once, from beginning 3rd straight into 5th?
Or did you mean to say he's currently a 4th grader, he took the iLEAP at the end of 3rd (in which case, it's not out-of-level testing), and you're looking at skipping him from 4th to 5th, a single skip?
I'd say, first of all, that you should consider yourself fortunate that the district is giving him out-of-level testing (I assume they're using the LEAP) at all, because my DD's schools refused to even consider a skip, much less test her for eligibility for it.
As for the materials he hasn't been exposed to, we solved that problem through a homeschool year.