If instances of Config are being instantiated manually via new, then Spring isn’t getting involved, and so the annotations will be ignored.
If you can’t change your code to make Spring instantiate the bean (maybe using a prototype-scoped bean), then the other option is to use Spring’s load-time classloader weaving functionality (see docs). This is some low-level AOP which allows you to instantiate objects as you normally would, but Spring will pass them through the application context to get them wired up, configured, initialized, etc.
It doesn’t work on all platforms, though, so read the above documentation link to see if it’ll work for you.