If you're looking to stop people voting more than once then you don't need SSI. The poll appears on everyone's browser and when they click on an option they're passed to a perl script right? If so, then its just the perl script that needs to access the REMOTE_ADDR. If they've voted before then you politely tell them where to go. If you've not seen them before you count the vote.

The only reason I can see for using SSI would be if you want to stop people who have voted from seeing the poll a second time. If this is what you're trying to do then SSI should have all the ENV vars available anyway, just use the script name in your SSI ('script.pl'). If you tell the SSI to execute 'perl script.pl' then it will be run in shell and will not have the ENV vars you need.