32 minutes ago, Soupcon said:Recipes need to have rice flour as an ingredient.
Rice flour, in a recipe with some water, might produce a crispier and product, but, in this recipe, it's not going to lend the shortbread any structural integrity.
Some form of liquid (water, egg, etc.) would be the most sure fire way of gaining handling ability, but it would also risk toughness, and also perhaps stray from authenticity. I would bet you any amount of money that Walker's get's an end product capable of being shipped by pressing their cookies. If your baking pan is stackable, you might try pressing down on the shortbread very hard with another pan. You could also find something rigid, square and flat that you could use to tamp the shortbread in the pan. That might give you the structural integrity you're looking for.
Or, you could try water- perhaps with a very fine sprayer. But, like I said, be careful.