Make all your polls 'Members Only' and it won't set any more cookies. You have the option of setting a poll to 'Member Only' when you create a new poll. Or you can edit a poll and make it Members Only.
How can I change the default setting to "Members" ?
Login as Admin. Go to the Poll. Click on the Edit the Poll icon. Change the "Who Votes" from Everyone to Members Only. Click on Post Changes at the bottom.