RoundCube login override needed

I need a hack to RoundCubes normal login process. Currently its like this: if pass for email@somedomain matches hash then login I want to change that to: if pass for email@somedomain matches hash then login else if a hash exists for _admin@somedomain |Begin Indent| if pass for _admin@somedomain matches hash then login else display error |End Indent| else display error The script must use the same domain, as multiple domains and _admin@ emails will exist on the system.