If you want gf York puds it's just cornflour ( Americans call it cornstarch)eggs and any milk even dairy free . Ensure tin is oiled and red hot 3/4 fill and do not ope untill cooked around 18-20 min on 200 . I use 100g cornflour 3 medium eggs or 2 large and around 130-150 mils milk . And good pinch salt . Mix recipe till it suits your size eggs and cornflour and adjust liquid . Eggs to flour slowly beat in milk . Don't let it stand long mix when ready to add to tin should get around 12 in muffin tins . Good luck .Mr sowerby

if your friend can eat spelt (which is to say your friend is wheat-intolerant but not gluten-intolerant), i would try that first, as it isn't wheat but does have gluten. your best bet would be white spelt flour, which i've seen sold in bulk, though i've never looked for it pre-packaged.

I would just add that Gluten Free Girl (http://glutenfreegirl.blogspot.com/) is my favorite source for all things gluten-free. For dessert-specific GF ideas, Cannelle et Vanille is also a fantastic resource: http://cannelle-vanille.blogspot.com/.

Buckwheat flour is on the heavy side as far as flours go; it also doesn't contain an agent to help hold everything together (regular wheat flour contains gluten). I would use white rice flour, since it's the lightest of gluten-free flours and yields excellent results in baked goods that mainly use eggs as their leavening. (I use it when I make a souffle.)

You still need to add something to help it hold together. Sweet rice flour works very well. I use it in equal part with white rice flour to replace the regular flour. Anyway, my mixture for 1 cup regular flour would be:
1/2 cup sweet rice flour
1/2 cup white rice flour
2 Tbls tapioca flour/starch

If you don't mind them a bit heavy, you can try replacing the white rice flour with buckwheat flour. Make sure to keep the tapioca flour and sweet rice flour or they won't work properly. I've never tried Yorkshire pudding with a heavy flour, though, so no guarantees on how it'll work.

Or, take the easy way out and get a gluten-free all-purpose flour replacement. King Arthur Flour makes the best one I've tested so far: http://www.kingarthurflour.com/glutenfree/

How about trying with gluten free self-rising flour which is also wheat free. Here is a recipe link: http://www.food.com/recipe/yorkshire-pudding-gluten-free-42105
I'm guessing you are from the UK, and there is a brand called Doves Farm that carries the flour. Here is a link with a recipe for the flour if you can't find it pre-made: http://www.ellenskitchen.com/faqs/glutfree.html

How about cooking some potatoes and carrots with that roast instead of making the pudding?