Gluten-Free baking question...

Sorghum sounds like a good choice, but I'd be more apt to choose Buckwheat (yes it is Gluten Free and no it isn't actually wheat). Buckwheat has a nice flavor in and of itself, and I think would enhance the flavor of the currants already in the recipe.

If you can eat nuts/almonds, you can grind them in a food processor, just enough to make a fine powder, not nut butter.

For that recipe, if you can't do any ground nuts or nut flour, I'd just sub sorghum flour for it. That's a whole grain flour, nutritious, and it's a little denser than rice flour. It'll change the texture of the recipe slightly, but probably not so it'd be noticeable. Sorghum has a relatively neutral flavor as well; it's a little nutty and a little sweet, but shouldn't cause a problem with the overall flavor profile of the bread. Have fun!