I don't use LOTF or CoEmu but I know the quest has been release. This structure of the item packet is for the Jar. You have to find the method for adding a soul in the jar. I'm on the older client, I don't want to take the time to search...
Code:
Length -> UInt16 //I think it's 36 like the other
Type -> UInt16 //0x3F0 or 1008
UniqId -> UInt32 //Random Number
ItemId -> UInt32 //750000 for the Jar
ToKill -> UInt16 //0 to 65535
Type -> UInt16 //1 to 20 (Monster)
SubType -> UInt16 //0x01 -> AddItem
Position -> Byte //0x00 -> Inventory
The packet can be not complete. I just have take the time to check my idea about this item.