The 21-year-old won the Dutch MotoGP at Assen in June and still has his home Australian round to come.
American Hayden, who won the 2006 title with the works Honda team, finished third at the inaugural Motorland Aragon race on a Ducati in 2010.
The 35-year-old started 216 races between 2003 and 2015, winning three.
"This is an unusual experience for me because I’ve never been a stand-in rider before," he said in a statement.
"But I have a good relationship with Honda...so it is nice to go and help out another Honda team.
"I'd probably be riding motorbikes anyway and I would definitely be watching the race on TV, so I might as well show up and have some fun."
(Reporting by Alan Baldwin, editing by Ed Osmond)
