In SSMS set results to text and run (replace DOMAIN\login_name with appropriate values):
select 'USE ' + name + '
GO
CREATE USER [DOMAIN\login_name] FOR LOGIN [DOMAIN\login_name]
GO
EXEC sp_addrolemember N''db_datareader'', N''DOMAIN\login_name''
GO
'
from master.sys.databases
where database_id > 4