Sephiroth was not possessing the clones (now the "clones" which are just called "clones/copy/replica" but simply have JENONA S-/G-/A- cells injected). He just called them. Which is why Cloud even followed him subconsciously and not only because he wanted to. However as Cloud says Sephiroth would have no problem to use the clones. That's why he decided to get the Black Materia with Cait Sith's help.
Sephiroth is present in all of those bodies with his consciousness but in the clone (hooded men/Cloud) bodies only more subconsciously to lead them to the crater. He only uses JENOVA's body and his own body in a greater way. He can control the cells and does as he mind controls Cloud but he does not really wander around inside of them actively as he does with JENOVA's body.
"Possessing a broken, imperfect form like that seems pointless anyway; Cloud was a much better choice."
Fully using his own consciousness, so fully animating a body it would have been irrelevant. If it is Sephiroth himself living inside of a body he can use his powers as it comes from his will - his greatest power.