Wheat-free bread with added gluten?
I've never found wheat gluten flour that was higher than 80% gluten which is what I use, adding some when I make bread with rye flour. But if you can't eat wheat due to high fructans content, would you still be able to digest the fructan in the other 20%? You wouldnt be adding much gluten flour so the small amount of fructans might be okay.

Rather than buying and using standard gluten-free flour which is quite expensive, why not mix up your own? It's easy to. I've made gluten-free bread a few times for a friend who's since moved. The wheat-free flour mix that I made was rice flour, tapioca flour, potato flour and coconut flour in the ratio 3:3:3:1. You can then add gluten flour to this mix if you still want to try using gluten instead of xanthan gum. Xanthan gum is added to all gluten-free bread flours to help the dough keep its shape while rising. It's not needed if you plan on adding gluten though.

Bread flour is normally 10-13% gluten. Trouble is I don't know if that's by volume or weight. Maybe someone reading this knows and can tell you. If it is by volume, then replacing 2 tablespoons of the flour mix with 2 tablespoons of gluten flour should give you roughly the right gluten content. Hard to be exact as it's possible gluten flours vary in their actual gluten content.