What I have to say here won't help to create many gmail accounts, but it's very useful for general signups where you want to use a disposable email account but signup won't accept the address. Create a gmail account but set up the forwarding on it. I have a gmail that forwards all mail to a disposable mailinator account, but it''s possible to setup filters that forward only specific mail. This was awesome for creating fake Google Group accounts, nowadays it's useful for signups that don't accept mailinator.