Hi Nicolas,
when using SAP GUI you could map several SAP backend users to the same AD account. The system would then let you decide at login which backend user your want to be. However, this only makes sense if there is a limited, known number of backend users for each AD user. Also, this only works in SAP GUI, not in the browser or NWBC. So it should not be the basis of a long term SSO strategy.
Best regards,
Christian