NOTE: Store this encoded file somewhere safe (like your user profile dir)
PS> ConvertTo-SecureString -String "NotARealPasswd" -AsPlainText -Force | ConvertFrom-SecureString | Out-File C:\passwd.txt
RunAsScript.ps1 <- combine this with: Powershell (double-click -> run)
$pass = get-content C:\passwd.txt | convertto-securestring
$ssmsPath = "C:\Program Files (x86)\Microsoft SQL Server 2012\120\Tools\Binn\ManagementStudio\Ssms.exe"
$credentials = new-object -typename System.Management.Automation.PSCredential -argumentlist "MYDOMAIN\dsomething",$pass
Start-Process -FilePath $ssmsPath -Credential $credentials