With personal choice dining there really is no other way to tip.
You're right, but the solution to that problem is easy -- just drop personal choice dining.
Realistically, though, there is another alternative. You could tip your waiter each night, either in cash or by cabin charge. It would be easy enough to provide each diner with a form to charge tips for the waiter and the assistant waiter to his/her shipboard account.
Here's a sample of the form (which probably won't display correctly, but it's worth a try...).
| Tipping Guidelines: Tipping, of course, |
| is a matter of personal discretion. In |
| response to many passengers who ask how |
| much is customary, Princess provides the |
| following guidelines. |
| * The waiter normally would receive |
| $3.50 per passenger per day. |
| * The assistant normally would receive |
| $2.00 per passenger per day. |
| Table No. ______ |
| Gratuity for Waiter $________.____ |
| Gratuity for Assistant $________.____ |
| Total $________.____ |
| Signature: ____________________________ |
| Cabin No. __________ |