There is a product called interior coat its used for refreshing or changing the colour of vinyl seats in classic cars, I have never used it and do not know how well it works.
It is supposed to penetrate the vinyl and change its colour its available in black and I think simply sprays on, its ?12 for enough to do 1 sq. metre and if the vinyl is not ripped it has to be worth a try.
You can get it from Frost automotive at
www.frost.co.uk
Hope this helps let us know how you get on?
regards steve