The solution here would be a "tipping purse." A user would allocate a certain amount to that specific purse - perhaps 20 or 50 STEEM - and they would be able to use that purse for tipping without the need for a password. How much they keep in there is directly under their control and would only require them to be signed in under their posting key in order to tip. Filling that purse would require either the private active or owner key, like any other wallet transaction.

If you don't do a lot of tipping, or if you're active every day, you don't need to keep a lot stored in that purse when you're not using the platform. Top it off when you're going to be active and even transfer the funds back to your main wallet when you know you'll be away for an extended period of time. It can be easily managed.