matching multiple usernames with Boolean rules in NCM policy

I'm trying to do the following in a NCM policy rule:

Config File must contain:

username alice

OR

username bob

AND

Config File must NOT contain:

username [anything except alice OR bob]

I tried to use a regex negative lookahead to make this work:

Config File must contain RegEx expression ^username (alice|bob)\s

and Config File must not contain RegEx expression ^username (?!(alice|bob))\s

but it doesn't. It matches the first part fine, but it doesn't alert if I have "username test" in the config.

Help?