Single entry visa wants to visit HK

Hello
I am a UK national living in Guangdong (close to Guangzhou) and my friend is staying with me for 2 weeks. He wants to visit Hong Kong and we even booked tickets and accommodation before realising that he only has a single entry permit to China. His flight back to the UK is Tuesday 9th Feb from Guangzhou airport. We didn't travel to Hong Kong this morning because I am afraid he wouldn't be able to come back to take his flight. Is it possible to go to Hong Kong and then get a 72-hour free transit to come back into mainland PRC for a couple of days before he departs? We would be travelling to Hong Kong and back by ferry or bus (we're not planning on flying). Or, could it be possible to go to Hong Kong and travel from Hong Kong airport directly to Guangzhou airport on Monday 8th on a 24-hour permit? We have already reserved a room at the Guangzhou airport for that night. In this situation would we be able to leave the airport to stay in the hotel? Any advice you can offer would be much appreciated. Thanks. Kind regards
Jessica