What I do with stir fry is when the food is cooked, all the seasoning are in, I grab pinches with my finger and thumb and dust as little into the boiling liquid at a time as I can stirring vigorously. Thickening happens a little slower with no clumping. The other way is to use the same technique but into a little bowl as you mentioned. But sprinkle with pinched fingers whisking vigorously at the same time. It takes about 10 minutes to fully thicken and will thicken more when it gets heated. Tricky for sure but not bad if you get the hang of it and not a yuck mouth feel if you don’t over add it. Easy to put too much and end up with a clumpy mess and this works best for me. I use about 1/8 teaspoon for a stir fry, usually I don’t need more. You can also make roux with it, doesn’t take much and it will brown much faster than flour so you have to be watchful.
1 1/2 tsp. Xanthan Gum
1 stick of butter or half cup of fat