Allow same username/account on similar URLs in Vault

I visit a number of websites that have separate logins for sites that are on different subdomains. Some of these sites want me to use the same login I use on the main domain's website, however demand that I use a different password from the main domain's login. Norton's Vault will not let me save passwords on a subdomain if the username is the same as a login on another subdomain saying that the username is already in use. I would like to be able to tell the Vault that this particular domain uses subdomains so I can save multiple same usernames with different passwords.