nice try but he hires actors to pretend to be supporters at his rallies.
>pay people to support him in polls
That is illegal. I don't think his campaign would risk it even if he could mostly get away with it. The press would have field day. Realistically I think the most they could do is bribe people with 'gifts' of food at rallies and/or transportation on their way to the polls.
This is a thing that's happened as long as there have been rallies.
More common, though, is trading favors. A lot of candidates will cut deals with local labor unions to get them to send their members to pack out the stands for the cameras.