You can try something like this. Use InteractByGossipOptions="x" where x is how far it is down in the list. Separation by commas - specifies which stare number to choose on each page of communication. Theoretically it should work.
<PickUp Nav="Fly" QuestName="Quest Name" QuestId="Id" GiverName="NPC Name" GiverId="NPC Id" X="" Y="" Z="" />
<While Condition="!IsQuestCompleted(Id)">
<CustomBehavior File="InteractWith" QuestId="" MobId="" InteractByGossipOptions="X,X,X" WaitTime="X" X="" Y="" Z="" />
</While>
What is the ID of the quest?