I’m pretty sure that normal dialog would simply be “… filling in for Marty Moon.” No adverb required. If an adverb were desired it should be temporarily rather than indefinitely since it was specifically a two week suspension. Indefinite suggests no one has a clue when Marty will be back, and if the station manager plans to boot Marty you don’t even need to do the filling in line, you just introduce yourself as Jackie Carter.
I’m pretty sure that normal dialog would simply be “… filling in for Marty Moon.” No adverb required. If an adverb were desired it should be temporarily rather than indefinitely since it was specifically a two week suspension. Indefinite suggests no one has a clue when Marty will be back, and if the station manager plans to boot Marty you don’t even need to do the filling in line, you just introduce yourself as Jackie Carter.