Just tested this, sadly keeping only 1 quest instead of 4. Anyway the trick is simple:
The quest Hallow's End Treats for Spoops! involves four others mini-quest
- Flexing for Nougat
- Incoming Gumdrop
- Chicken Clucking for a Mint
- Dancing for Marzipan
All of them can be taken again upon completation but not turned (because you already posses the reward).
Take all of them again upon every completation, turn in the main quest giving the four quest rewards back.. THEN go back to the four previous NPCs and get credit for some free quest =)
Hope it helps