The original requirement for T-12A was to allow the T-12 to have a decent safety margin of thrust on a hot, Wittering summer day. There were concerns with the T-10s hover performance so the study was done as to whether it was worth putting a Pegasus 107 (of which we only had limited numbers) into a T-12 rather than a 9A for Afghanistan.
I seem to remember seeing pictures of the personnel pod on Navy News, attached to a Sea Harrier. It looked rather snug.
For more fictional Harrier exploits James Bond flies one in the novel Win, Lose or Die by John Gardner.