Hi Josh,
There is no way to change this with a simple set of a property. What do you think to open a improvement issue on support.liferay.com?
If you have urgency you can change the following line
1String login = LoginAction.getLogin(request, "login", company);
of the html/portlet/login/view.jsp file to
1String login = LoginAction.getLogin(request, "login", company);
2if (Validator.isNotNull(login) && login.startsWith(StringPool.AT)) {
3 login= StringPool.BLANK;
4}
I think this will solved your needs
Regards