I'm not sure, but the seed pods on mine are already dry and cracking open and that is when ordinary lupin seeds are ready to sow. Seems to me it would work for the tree lupins, too. Someone else might know more.

Lupin seeds need cold to help germinate. I would broadcast some now over the area where you want them and keep the rest in the fridge till March, then germinate them in a greenhouse to kick start the seedlings - those you broadcast will self seed slower, so you will end up with a longer flowering season.