More than 1 poll vote per IP address?

I’m using Lester ‘GaMerZ’ Chan’s great poll plugin, and it works fine. However, some of my readers have written in with the following complaint: Say I’m running a poll and both the husband and wife in the house want to vote. But because they share a computer and thus an IP address, only one of them can vote.

I currently have the poll options set to log by user name, but apparently cookies/IP are still determining who can vote even when cookies have been cleared.(?) Is there a way around that?