I'm looking for discrete emotion manipulations that distinguish different low-arousal, negatively valenced emotions (e.g. sadness vs. disappointment, vs. guilt vs. boredom).
I suggest you take a look at the PANAS-x (expanded form). There are a lot of low activation mood words in the Negative Emotion Scales section.
Watson, D., & Clark, L. A. (1994). Manual for the Positive and Negative Affect Schedule (expanded form). Unpublished Manuscript. University of Iowa. Iowa City.
The following article (reference, link to manuscript, link to website) evaluates a host of film clips and provides affect scores for each. You'll likely find a clip suitable for your desired manipulation.
Schaefer A, Nils F, Sanchez X, Philippot P (2010) Assessing the effectiveness of a large database of emotion-eliciting films: A new tool for emotion researchers. Cogn Emot 24: 1153–1172.