Now it's breaking the 7-line rule
If you changed "discard a possession borne by a companion" to "Free Peoples possession" it would fit, if made slightly less thematic for opening the field to support area cards.
"If the fellowship moves to an underground site, discard a
card to make the Free Peoples player exert a companion or discard a Free Peoples possession.
You may play this event from your discard pile; place it beneath your draw deck instead of discarding it."