I wouldn't use epoxy. I would braze it. I would use tubing from a scrap frame made from oversize tubing. This will probably still need some bending to get it to fit perfectly.
You could do it if you really wanted to, using a swirl-flame "turbo torch" and mapp gas, but you should practice on some scrap first. Use Harris Safety-Silv 56 and black flux.
I would put the flux on, assemble it, then put on a couple of hose clamps to hold it all together and tighten them well to minimize gaps. A properly-shaped part would be critical. You'd probably spend a hundred dollars and 5-10 hours to get it right, but you'd learn a new skill and you get to keep the tools.
__________________
Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.