Use Windows Credential Manager.
Create a new Windows credential with the following details:
- dbservername.domain.com:1433
- domain\UserId
- Password
Also create a shortcut for SSMS with the following in TARGET:
C:\Windows\System32\runas.exe /user:domain\userid /netonly "C:\Program Files (x86)\Microsoft SQL Server\100\Tools\binn\VSShell\Common7\IDE\Ssms.exe -nosplash"