Hello,
Partial scoring is only available for MCQ type of questions in Captivate.
If you are willing to create custom FIB slides, this will be possible. You'll use validated Text Entry Boxes, that can have a score attached, one for each blank. I have explained such a FIB question slide with widgets (TextArea) but the problem is that scoring is than much more difficult if you want to report the score. Perhaps you could have a look at:
http://blog.lilybiri.com/widgets-and-custom-questions-part-2
http://blog.lilybiri.com/extended-textarea-widget-more-functionality
Lilybiri