How do we explain to Bob that he doesn't get his donut without resulting in a fist fight, a discrimination lawsuit, an all day seminar on the technical workings of the blockchain, giving away a free donut, and/or potentially losing Bob as a regular customer?
You probably won't be able to so the only solution is to prevent it from happening to begin with.
Honestly until tx ids are immutable, the use of unconfirmed change outputs is just going to cause mass chaos.
The client waiting until change is confirmed isn't "ideal". The ideal solution is to make tx ids immutable but that is a long term fix. In the interim a user (possibly) having to wait for the change to be confirmed is far superior to transactions randomly breaking and non-technical users and merchants trying to figure out why it seems to just fail randomly. The later is just going to kill adoption.