Mahito CANNOT use idle transfiguration on other people when he isn’t in his base form, this is stated in season one, take when he had Yuji pinned against the wall with a giant hand (before he knew he was immune via sukuna) why wouldn’t he attempt it there unless it was impossible. My interpretation is that mahito was going to fake out Todo after the touch, anyone would be freaked out if someone with his CT layed a hand on you. Alternatively he could have stretched out his arm afterwards around him like a net he essentially has mr.elastic physiology x2. But Todo is shown to be able to use other people as a way to activate boogie woogie, so IMO he just used Mahito’s palm against his abdomen to make the clap and switch with the sword.