Minogue told The Sun that Baby Spice has been "one of the best guest judges ever".
The Aussie star is mentoring the over-25 hopefuls in her pad in St Tropez and said Bunton, 32, had helped her enormously.
"She's been brilliant, one of the best X Factor guest judges ever. She really helped me focus on who we should be putting through to the next round. Emma is one of the biggest X Factor fans so she knows the show inside out."
Minogue said the decisions they faced were heartbreaking. "It’s so hard deciding who to put through and who to send home because it means the world to these people. You’re sitting there and you’re in charge of these kids' hopes and dreams," she said.
At nearby Cannes, Cheryl Cole has turned to Girls Aloud bandmate Kimberley Walsh to pick the best of the girls' category, while Louis Walsh has picked Westlife singer Shane Filan as his helper.
Simon Cowell's regular guest judge Sinitta has returned to help him whittle down the boys' category.
Cowell recently confirmed reports that Britney Spears will be among guest acts to feature on the show.