I think it is impossible. At least not without some serious collateral damage. The problem lies in the idea to send “all” pedophiles to an island.
First you would have to determine who is a pedophile and who is not. That could prove to be tricky. However the last decade some promising ways of identifying a pedophile have emerged. Brain scans, implicit association tests, measuring penis enlarging tests and psychological reviews all claim with a certain degree of accuracy to do the job. But some pedophiles would still go undetected. And of course you would also have false positives. People of whom the tests show that they are a pedophile but in fact are not.