If it ever happens again...
Just take a scissors and cut the back half of the pinky off (assuming it is not a live pinky). Messy, but it works. Your snake is less likely to regurge if the item is not oversized. If he is able to digest it without regurging, then it may not be too big. If it does regurge, DO NOT feed again until you read the regurge FAQ on these forums.