I'm pretty much in agreement with mouthymerc.
Since Sam's answer does indicate the character has the option to use the talent or not, the player decides before the dice are rolled when the critical injury modifier is being rolled. Once those dice hit the table, the player has to accept the result.
Not what I would have expected as far as whether using the talent or not is a choice on the player's part, especially as it's a Passive talent.
Edited by Donovan Morningfire