Well, I suppose same way you reduce spam and abuse anywhere else.

Raise the cost enough it's not worth it. Some middle ground could be requiring mailed in applications. That's a marginal cost for a real applicant but a higher cost for someone trying to send swathes of applications out.

It might seem backwards but there are plenty of solid non technical solutions to problems.

You could also do automated reputation checks where a system vets a candidate based on personal information to determine if they are real but doesn't reveal this information in the interview process.

That's how all government things tend to work (identity verification)