What you want to do after jointing the first pass is to fit a 1/4" ply
sled to the partially jointed part and run the workpiece and sled
through your thickness planer to flatten other side. Then, flip the board
over and without the sled run it through the thickness planer to flatten
the originially jointed side.

Can you please clarify the part about the 1/4 ply sled?
I cannot visualize where and how it is attached, and precisely what it does
Thanks