For any other FTers (particularly DL flyers that are not super familiar with SYD) that find this thread:

Turns out that we *do*. On landing at SYD international, there is a transfer desk, outside border control, but inside the I terminal. Here you can get a BP for your domestic flight, drop your bags, and if necessary, reiterate that you are a DL whatever. I do not know if they would have gotten this already because I had my DM card out and ready to show from the beginning.

From there, there is a private-to-VA shuttle bus that goes over to T2 at the curb landside. There is a separate entrance for elites that has a private security screening and dumps you right out into the lounge.