In a sneak peek on Wednesday morning, titled 'Surprise Contestants', Block host Scott Cam says he has a reserve team ready to go should Sara and Hayden decide to leave.
Karl and Georgie then appear wearing hard hats and hi-vis gear, as Scott says: 'I can't believe that you guys have volunteered to be the replacement couple!'
To much laughter, Georgie replies with: 'Right on cue, Scott!'
Karl and Georgie are then shown around the Gatwick hotel work site in St Kilda, before they meet other contestants.
Scott then asks the pair of what they think of their 'new project' - Sara and Hayden's unfinished apartment.
Georgie says, 'I'm liking it, I'm liking it. I'm liking the dimensions, I'm liking the natural light, Karl.'
'The light is perfect,' says Karl, as he looks around the room.
'I'd be going for soft greys, I think, in terms of colour palettes,' adds Georgie.
However, it seems Karl and Georgie's work-site visit was only temporary.