Shortening substitute that can prevent gluten growth?

Every fat prevents gluten formation as much as any other fat. At least, if there are any differences, they are not noticeable by somebody eating a finished product.

When substituting fats, "how much it inhibits gluten" is not a criterion. Just pick whatever fits your recipe.

I frequently use lard in my biscuits and pie crust and the texture is always light and flaky.

However, the temperature of the fat is very important. This applies to shortening as well.

If I use the lard at room temperature the result is much less flaky than if I chill (or usually, freeze and shred) it. Gluten formation is inhibited at cold temperatures. Once the fat and dry materials are mixed, I return them to the freezer until the last possible moment. When you add your (also cold) liquids the gluten doesn't form as quickly.

As an added bonus the cold temperatures also inhibit any leavening agents in your pastry. If multiple batches are needed, store the shaped dough in the refrigerator until you're ready to put it in the oven.