Poll question

[putttee]

I've been messing around with the poll tool a bit and have one question that I dont seem to find an answer for. I do host contests where the members can vote for the winning contribution and i want to be able to keep track so no one creates multiple accounts to win them. I used the make voters public option but that makes it open to every one to see. I do want it limited to mods and admins only. Is there any way to do this as is or does it required modifications. If it does have anyone done it and can tell me how?

Thanks in advance