look you on youtube. you take a razor sharp blade and slice right down the middle of the anemone. i've heard of it and some1 on a local forum did it every 2 months. he had a 20g long with 20 anemones. so it is possible just beware of the risk your taking and possibily killing it.
Only anemones that split in the wild, can be split. Nems like carpets reproduce sexually and have not been successfully split in captivity. The only one that I know of that is successfully split on a pretty constant basis are BTAs. But they still need a lot of care after being split.