Actually the PF usually has only 2 hands, one on the controls or steering and the other on the power levers.
Which is why the off/on bits are better done by the support pilot.
This has always made complete sense to me and was how we operated in my former (Boeing) company.
In my current company (Airbus), we make one exception. The PF turns on the Autopilot rather than calling for the PNF to do it.
I've never understood the rationale for this odd exception...that the PF should take his eyes off the flight instruments, and his hands of the thrust levers, in order to reach up and select an autopilot on.
Not a major point, of course, but not really in line with the general philosophy that a PF, when flying manually, should do nothing except fly.
PG