My card declined last night due to insufficient funds (my fault - I forgot to move money across from my goals).
TL;DR: Post decline, my friend was stuck in a taxi with an angry driver until the fare was paid. As the journey was linked to my card, I had to make a phone call to pay over the phone while she waited. This took 20 whole minutes. So embarrassing.
Anyhoo, to ease any future humiliation, it would be great if I could apply a setting that allows a goal to act as a backup when my main account has insufficient funds.