Steemtipper.com acts as a proxy wallet for those people on twitter who don't have a Steem wallet. If they don't set up a Steem account, they can just use the tips they receive and claim to tip other people. If they do set up a Steem account then they can withdraw the Steem to their wallet. I think in the near future they are going to add additional platform bots and possibly even account creation.

So basically you can just tip to whomever you want on twitter. If they don't login and claim the tips within 7 days, they're refunded anyway. If they login and claim them, they can keep them and spread them or set up a wallet.