Just in the same way.
If you run graphical interface of bitbar, you can type 'getnewpubkey' in console (I guess it's Help->Debug window->Console).
Also, you don't need to specify a public key if you run your own p2pool node. It will automatically request a pubkey from your bitbard and generate payouts to it. You only need to specify your pubkey if you connect your workers to a node run by someone else!
OK, cheers. So how long until payouts start from my own p2pool node?
Go to http://localhost:
P.S. The payout value is roughly proportional to number of your valid shares.