Question about Outlook Express

Using Applescript I can get the user name in Outlook 2011, but it will only display the text that comes after a backslash if present in the user name field.
With this Applescript I can get the user name from Outlook:

tell application "Microsoft Outlook"
    get the user name of exchange account 1
end tell

result--> username

But in the Outlook Account it reads:

ADDOMAIN\username

If I use Applescript to enter a user name it just appends the user name to the ADDOMAIN\ text

tell application "Microsoft Outlook"
    set the user name of exchange account 1 to "username2"
end tell

In Outlook account settings will result in:

ADDOMAIN\username2

Is there any way to clear this invisible text using Applescript?  I need to deploy this to 1000+ users so using Applescript is the preferred method vs. going to each user's computer individually.