Instead of stacking the bolts upright vertically, how about laying them down side-by-side on the table. That way you won't have to worry about them falling over and people can still see each fabric individually. I make a beeline to anywhere I see fabric, whether it's up, down, or stacked so I don't think you'll have a problem attracting customers, I personally can spot a bolt end a mile away.
Then you could use anything with a little weight to hold the ends, a couple of bricks, a block of wood, those old metal bookends you see in offices with the lip on the bottom that goes under the books would work really good.