How do I filter my contacts on a given campaign based on IP address?

How do I filter my contacts on a given campaign based on IP address?

In other words, I would like to do analysis of my mailing list based on country/IP address.  I would like to create segments or a new mailing but only to folks in Denmark or with an IP address associated with that country.  How do I do this?  The country is not found in the associated data in the CRM.