Way I see it is that you've got two separate issues - getting yourself out of the US and getting back into Australia.
The declaration thing really only applies to your arrival back here, and should be OK if you've got it labelled and can recite the Customs regulations to the inspecting officer (who may not be up to speed with regs concerning odd stuff like hops that to him might look and smell like dope).
But first you have to exit from a US airport, so I'd also be concerned about sniffer dogs patrolling the departure lounge areas. Given that hops and cannabis are from the same plant family they may (to the doggy) register as the same thing (why do I think of Amarillo in particular?).
If a dog did register a contact with you (smell of hops on hands, clothes, shoes) or in your bags you could be taken off by security to an interrogation office be questioned and a fuller search made. You won't be alone - major US airports must process dozens of people a day under similar suspicions. Consider that if you get pulled in you might be delayed and miss your flight, and would lose your fare money if its one of those cheapo take-it-or-leave-it fares.
That said, I understand that different dogs are trained to detect different contraband substances. So I guess there might be more of a prevailing focus on detecting narcotics and explosives than cannabis. So there might be only junkie and cracker pooches on patrol.