Global proximity sorting using GMAP - Is this possible?

Does anyone know of a way to utilize the location module to conduct proximity searches internationally, based on some criteria other than Zip codes?

In particular, I have a series of classified ads that each have a unique location; it would be helpful to sort these posts using a proximity filter in Views on a global basis, rather than just limited to those in the US, UK and a handful of other countries that have available zipcode data.

Thank you!