Hi @Ben Harper
I don't believe this is possible, although if it was it would be something I would look to do myself. The point of sending the link to the invoice is to allow it to be tracked properly by QBSE in terms of when a client views it, which I don't think would be doable if the system just attached a pdf to the email.
Downloading the pdf and sending it manually is a bit of a fiddle and then causes further work with having to send the email link to yourself so that you can mark the invoice as sent in QBSE and further process it when it's paid. There's no way to do that if you just send the pdf manually.
Sorry that's not the answer you were hoping for. I've thought about this one a couple of times myself.