Have a read through at Tip - Action Override User settings for tips
Assuming the username & password has Administrator access on the machine, and the BigFix Operator knows the account and password to send, you could probably use scenario 7
override wait
runas=localuser
user=domain.com\user
password=required
asadmin=interactive
wait powershell.exe -ExecutionPolicy Bypass -File "{parameter "scriptPath"}" "{parameter "commVault"}"
The Console prompts for the password when sending the Action; the Console operator must input the password to use.
I haven’t found any combination that allows you to hard-code the user’s password, and still run when that specific user is not logged on to the endpoint.