Joint the board in sections and iterate through Left, middle, right side until reasonable jointed
but there is a risk that each section is not parallel.
Check often, adjust as necessary.
This is basically similar to the problem of how you face anything that is wider than the plane (a somewhat-common occurrence LOL). Because shavings can be on the ...
Alternative recommendation for smoothing without the need for planing stop: a cabinet scraper (card scraper)
The other answers look to the work holding issue very well, and can definitely be used with a smoother plane. However, if you are only looking to smoothen, then I recommend an alternative to the plane: a trusty cabinet scraper. Since it is easier to ...