Allow name tags or a different item to keep monsters alive in peaceful mode

Some rare monsters, like charged creepers or elder guardians, can be fun to keep around and put on display.  But if you ever switch to peaceful they despawn, and you feel like you lose some freedom with difficulty.  So what if there was an item that could prevent monsters from despawning in peaceful mode so the time it took to capture and name tag your charged creeper doesn't go to waste?