Your organization prohibits using the Global Administrator to activate the Office 365 Securlet, so you want to know if there are any alternative solution.
You can use the “Privileged Role Administrator” and the “SharePoint Embedded Administrator” roles instead of the "Global Administrator" role when activating the Securlet.
Furthermore, you can remove both roles from the account used for the activation, once the activation is completed successfully. Going forward, the Office 365 Securlet will use the Enterprise Application to send API calls.
However, please note that if you used the activation account's OneDrive URL for quarantine settings, you still need the license to ensure the OneDrive feature for the account provided is functional.