Paul -
Your chosen yeast may well out-compete the wild yeasts. Adding some
pot. meta. would likely help tip the odds further in that direction,
as it will tend to discourage wild yeasts more than commercial wine
yeasts. Other than using exteme measures to kill all the existing
yeast and start over from scratch, I'm not sure there is much else you
can do. Cold alone really doesn't work to prevent fermentation for
very long. But the wine is likely to be fine.

Doug