What if the Hendo hoverboard had a magnetic surface connected to it under the engines so that the current could always be occurring, would it then be free to float over anything?
Do you mean a surface under the board, connected to it? Like a sandwich?
That wouldn't work because the forces generated by the top half of the sandwich (with the magnets or whatnot) would be cancelled out by the forces pushing down on the bottom half. Newton's Laws. Same reason you can't lift yourself up in the air by pulling on your own bootstraps, to use an old expression.