Christopher Maloney, Union J, Jahmene Douglas and James Arthur are said to have laid down their tracks several weeks ago, according to The Sun.
However, only the top two acts will perform their tracks in the final in Manchester on Sunday, December 9.
While the choices of the songs have yet to be revealed, Union J are said to have recorded a cover of 'Skyscraper' by Demi Lovato.
Simon Cowell has announced that this year's single will raise money for children's charity Together for Short Lives.
"Together for Short Lives is such an inspiring and important charity for so many kids and their families who really need help and support," said Cowell.
The track will be released as soon as the final has come to an end on December 9, meaning it will not be released the week of the Christmas singles chart.
Previous X Factor charity singles have included covers of Rose Royce's 'Wishing On A Star', David Bowie's 'Heroes' and Michael Jackson's 'You Are Not Alone'.
Watch the 2008 single below: