Dont' give up too quickly... see function module AUTHORITY_ CHECK -> via the fixed System user you can call that FM in remote system and export an alternate user name to the FOR USER extention in the check. That can be the calling dialog user name for example. Then based on that result of the check, the fixed System user in the RFC connection calls RFC_READ_TABLE for the S_TABU_NAM name of the table or not - this then has nothing to do with it's own authorizations anymore, it is just taking care of the system task of returning the data or not.
Downside: The fixed System RFC user must have all the authorizations for the tables and if there are problems then it is confusing for the trace on the target system side, because fixed user is authorized but message says "No authority" etc.
Cheers,
Julius