How to grant many users access to the dashboards and reports on the same payee effectively?

[PerforsN]

I'm facing a challenge that I wanted to pass by the community.

Some groundwork; Participants in IM are dealer codes that identify the external business partner linked to the sale. If the same partner operates in f.e. the B2B and B2C segment, there will be two of those codes. Since one partner can have many codes, the email is not unique. IAS is configured to only force unique loginName. MFA is required as a policy making it's difficult for two people to login to the same "participant".

Is see a few possibilities:

1. Create new user with it's own loginName and add proxy relation in SPM.
   - I would have to also maintain EA permission, linking the new user to the position.
2. Configure IAS to force unique email; modify duplicate emails with plus addressing.
   - This would allow me to create many users with the same loginName.
   - I would need to adjust the EA transformations to use loginName instead of userId (duplicates?)
   - IM doesn't force unique email, can plus addressing be done ín the transformation but only for non-unique addresses?

Looking at my own thoughts, option one is probably the best. Did you ever face a similar challenge?