... Unfortunately, I can't tell how much rapport, because I was only missing one from the max value due to harvesting a mushroom, AND obviously, the single-use-across-the-whole-account thing is not repeatable... Can only tell he also commented "something something how exciting!" when I did it.

Edit: and yeah, it's... Something extremely unlikely to happen. I've done it because I have noticed the fragment I forgot to actually use while banking stuff in Rawl'kha, and been carrying it with me for months. If I used it right away, I def wouldn't have had companions out, if I've noticed it with a summoned banker, same, and if I had a different companion out (I usually have Sharp on that character, I don't remember why I even had Azandar at the time), well...

Hella funky thing to place rapport gain on...