That is going to be a challenge. It sounds like you are bronze welding (brazing) mentioning a torch but the principal is the same whether you are brazing or welding. Aim the torch at the larger material and let the molten filler material carry the heat to the thinner material. You will have to take great care not to let the torch play on the thing material otherwise it will overheat and at worst melt and almost certainly burn so badly the flux will not be able to keep it clean.
I suggest you get some scraps of material and practise your technique. This is going to take a bit of finesse.