[jQuery] Validation Plugin

[jQuery] Validation Plugin

People enter an address to lookup on a google map, this makes an
asynchronous call and will either return a lat/longitude or not. if
not, i want to display an error to the user that an address could not
be found.
How do I go about this? I've not managed to get it working using the
remote attribute as I really need to call a client-side js function
which will in turn make the async call. Any suggestions?
Regards,
Rik