switch on classic GL after upgrade to ECC 6.0

We are in the process of upgrading from 4.6c to ECC 6.0. We intended to use the classic GL for the start and switch to the new GL next year. However we inadvertently failed to switch on the classic settings during install. Is there a way to turn on the classic GL on the fly without starting over and reinstalling?

Any ideas would be appreciated.

Thanks,

Hubby