I want to make a fructose free one for my dad. I am not a fan of sugar substitutes, either. Karo doesn't have fructose but sugar does. If I left out the sugar could I use corn syrup only or would it not set up?
It would seem to me that controlling the total amount of water in the recipe will be the trick, so you'll want a crystallized or powdered replacement for the table sugar rather than a syrup.
I've not tried it myself, but you might try using dextrose in place of the table sugar. Dextrose is the commercial name for crystalline glucose, and I found it readily available on Amazon (https://www.amazon.com/Now-Foods-Dextrose-2-Lbs/dp/B008MVJKFU/).
Normally when substituting one kind of sugar for another, assume 7 oz (by weight) per cup of sugar specified in your recipe, then weigh out that much of your alternative. But there are multiple sources online that state dextrose is only about 70% as sweet, meaning you'd want to divide by 0.7 to adjust the quantity from sucrose to dextrose. Here's a typical reference, though there were many others with the same information: http://www.livestrong.com/article/534691-how-to-bake-with-dextrose/
I'd love to know whether or not it works! If you try it, leave a comment and let us know how it goes.