Runas user on other domain

The command below will let you run a program as another user on another domain.

runas /netonly /user:<domain>\<user> "<program>"

If you want to run SQL Server Management Studio 2014 you would use the command below.

runas /netonly /user:<domain>\<user> "C:\Program Files (x86)\Microsoft SQL Server\120\Tools\Binn\ManagementStudio\Ssms.exe"