You could always make something out of wood fairly cheaply and quickly. Just make a platform out of 2 long pieces of 2x4 joined by 1 piece in the middle like an "H" flat on the floor, then have two posts rising up with a support bracing somewhere (so kind of like a vertical "H" connecting to the middle of the platform). You can drill holes through each of the posts at the top and maybe again at the middle so that you can slide a round stick (like a wooden closet clothes hanger pole) in to hold your pex so that when you pull on the pex, it will unroll evenly, it's kind of like a cheapo contraption I made out of scrap wood to unroll electrical wire off of the spool so that it wouldn't be all twisted. I guess the trick would be to make the platform big enough so that when you pulled on the pex roll, the whole thing wouldn't topple over.
Again this is just a temporary cheapo solution and an extremely ugly one, but it'll get the job done! heh