I found an article by Frank Michaux in the July 1997 issue of Low Flying that had, what seems to me, a good solution to getting air into the footwell.
He took, from a Mark three Escort's dashboard, the far right and far left fresh air intakes with their plastic pipes and put one into each footwell.
Drivers side was installed in a cutout he made behind the pedals with the vent angled downwards. The vent was held in place with silicone sealant.
He claimed he had no water leakage.
Any reason why this shouldn't work? Could be sealed with duct tape for the winter.
Ken Sailor