I am not sure if I really understand what you are suggestion - but from the little I grasp - this sounds VERY DANGEROUS - please speak to an electrician


This said - I have read this page:
Heated Towel Rails at Victoriaplumb.com - Heated Towel Rails | Heated Towel Rail | Radiator
and it says:

"Each heated towel rail can be upgraded to an electric heated towel rail by adding the electric element which is offer on each towel rails product page. Just tick the upgrade box to include the element."

But in any case it sounds like it takes someone who really knows what they are doing to do this