Temporary Hit Points Do Not Stack
If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 temporary hit points when you already have 10, you can have 12 or 10, not 22.
So, the best I can offer you is this. You carry around a goblin, hogtied, in your backpack. After every fight, you punch him unconscious (You have to explicitly declare you are doing this...normally a monster reduced to 0hp dies instantly and cannot be stabilized. See PHB 198) to top off your pool of temporary hit points. You can't stack up a pile...but you have have a THP dispenser you can lug around with you to make sure you regularly stay at WIS+Level Temporary HP in between fights.
(Disclaimer: guildsbounty is not responsible for any alignment shifts you may incur by following this advice to torture goblins, or for extreme social ostracism due to the horrific smells emanating from your pack)