Gmail aliases with Ipad

Since upgrading to IOS7 and registering with Gmail for two step verification, I've tried unsuccessfully to set up Gmail to send from my Ipad 2 using business aliases. I'm using the app specific passwords from Gmail. It used to work fine when I created an "other" account using the aliases, alongside the "Gmail" account. I've tried the "Add Another Email" option that came with IOS7. The server rejects the outgoing messages.

Apple Support couldn't solve it. I can use the Gmail app but that doesn't allow me to attach documents.

Any ideas please?