"The Runas utility is primarily designed to allow administrators to logon as an ordinary user, but to invoke a seconary logon, without logging off, in order to run administrative tools with administrator rights and permissions."
The RunAs utility prompts for a password when run and can NOT be pre-configured with the password.
The Microsoft solution is to use the SU.EXE tool.
There is another alternative, if the task may be run in the backround:
01. Use Start / Programs / Accessories / System Tools / Scheduled Tasks to create a task.
02. Browse for a batch file, program, or schedule CMD.EXE.
03. Set the task to run One time only.
04. Set the time in the past by clicking the minutes and changing them.
05. Set the credentials of the user you want to run this background job.
06. Check Open advanced properties for this task when I click Finish, if you need to do step 08 or 09.
07. Press Finish.
08. If you scheduled CMD.exe, modify the Run line on the Task tab. This will force you to re-enter the credentials.
09. If you don't want to leave this task in Scheduled Tasks after it runs, check the Delete the task if it is not scheduled to run again box on the Settings tab.
10. In Scheduled Tasks, right-click the task and press Run.