Armstrong, who was stripped of his seven Tour de France titles in 2012 by USADA, will take to the roads of France on July 16 and 17 as part of a Cure Leukaemia group of riders led by ex-England footballer Geoff Thomas.
According to a report from the BBC, Armstrong will link up with the group of amateur riders who are planning on riding the entire race route a day before the professional peloton tackles each stage.
"We know Lance's involvement has split opinion so we've tried to be as respectful as possible," Thomas told the BBC.
"The stages Lance will be riding come toward the end of week two when I know all the [charity] riders will need some support. I know his arrival will give them the encouragement they will need to carry on with this gruelling challenge and in turn raise as much money as possible for blood cancer patients."
The organised ride plans to generate over £1m for charity, while Armstrong will take on stage 13 from Muret to Rodez and stage 14 from Rodez to Mende.
However, in March, Cookson stated: "I'm sure that Geoff Thomas means well, but frankly, I think that's completely inappropriate and disrespectful to the Tour, disrespectful to the current riders, and disrespectful to the UCI and the anti-doping community.
“I think Lance would be well-advised not to take part in that."