Can't cancel out of force of will after selecting to use alternative cost and target spell to counter

[NapoleonBorn2Party]

This is not a bug, but it would be nice to be able to cancel casting force of will after you chose to pay the alternative cost and selected the wrong spell to be countered on the stack. After selection is made, you are locked into choosing a blue card to exile from your hand. I assume this is also true for other spells with alternative casting costs like force of negation and solitude