Hi savvyxeus,
Regarding how to convert on-premise user to MEU, I suggest you visit our Exchange Server forum for better assistance. Our engineers in that forum are more professional to help you on the issue. Once you get answers, please feel free to post back if you need assistance on deploying SSO after Cutover Migration.
In addition, Exchange 2010 doesn’t support Staged Migration as the TargetAddress property can't be modified.
Best Regards,
Bruce Zhou