I doubt there's any substitute for ether because a lot of people have spent a lot of time experimenting with diesels, and I mean people heavily into world class competitions. The ether doesn't lower the ignition point of the kero but because ether has a flash point of -40 it ignites rather easily and this is where the flame comes from to ignite the kero.

One of the additives sometimes used in diesel fuel is Iso Propyl Nitrate (IPN) instead of amyl nitrate (or nitrite) and I know for a fact that a diesel will run on pure IPN because I tried a few drops in an old Mills 1.3 long ago just to see what would happen. It started first flick and ran out those drops quite nicely but I wouldn't suggest trying to make a fuel out of it even if you could find any.