All gates at IAD are airside of the same checkpoints (with the exception of IAB which does not apply to OP). Thus, he may walk / train / moon buggy from his domestic arrival to his departure gate. If he does not have an onward BP, he will need to obtain that at the lounge or gate. .

I would call EK to confirm that it will, as a backup, issue the BP airside because being sent landside can be a significant and time-consuming detour.