You dont have to upgrade everybody at once.
1. Upgrade SEPM to MR5
2. Export the package for Windows 7 clients
3.Then others at you own will anytime MR5 SEPM can managed older version clients of 11.0.4202.xx
or meanwhile install only Antivirus antispyware on windows 7 clients . Install Lusetup then SEP. it will work.