Consider drilling a clearance hole (5mm) and attach the rack with bolts and nuts instead of trying to thread the Ti dropout. Drilling a hole is a lot less demanding than tapping it. Just be sure the holes are positioned so the nut on the drive side clears the chain and smallest cog.

Note to Thinline: Why do you think Ti is toxic? It is extremely stable and is used to make artificial joints. Hot shavings are a hazard no matter what the material but there is nothing particularly dangerous about Ti.