Create new login and user in Source DB with readonly access to DB.
Use SP_help_Revlogin SP on primary server and from the output
copy your newly created login details, execute that on destination.
so you get same login on destination without orphan user if it is sql login.
DB user will get prapogated with next log restore on destination server.
Provide user details of destination server only with login pw details.
Other than that I think Read_Only DB is for the purpose of reading only and better keep it that way.
Kindest Regards,
Sameer Raval [Sql Server DBA]
Geico Insurance
RavalSameer@hotmail.com