The pair revived the hit sitcom for three special episodes last year (11) to mark its 20th anniversary, and one of the shows is themed around the sporting spectacular.
The crew decamped to the Olympic Stadium in east London to shoot scenes featuring Lumley and Saunders' characters Patsy and Edina jogging around the venue - but they had to install their own running track as the site was still being built.
Lumley tells U.K. morning show Daybreak, ""It was before anybody else had even been there - before the running track was really even put down. We had to put down our own running track for Patsy and Edina.""
The episode is due to air in the U.K. to coincide with the London Olympics, which launches in July (12).