Inserting pivot data without RelationManager

I have a multiple select on an edit page, has a

belongsToMany()

belongsToMany()

relationship.

I want to inject something to be saved in a column in the pivot table.

I found out that the relationship is saved in

HasState::getState()

HasState::getState()

, but could not find a way to inject additional data to it.

Tried

mutateFormDataBeforeSave()

mutateFormDataBeforeSave()

in the EditThing component, but that gets called after

getState()

getState()

, so no effect.

Any help would be appreciated.