Plastic piece that coolant flows through broke - help

2012 Outlander 650 (Gen 1). There's a plastic piece that sits on top of the head (also on top of the thermostat), I have no idea what it's called, but the coolant flows through it into the head.

Recently I had a severe coolant leak so we stripped the bike down and found that this plastic piece had a small hole in it. I've ordered a new piece, but it's not arriving until after a planned ride.

Two things.

1. What is this plastic piece called? I forgot to ask the dealership when I described it to them.

2. Is there any way to temporarily plug this hole so I can ride on Tuesday? It needs to be something that can withstand the temperature and pressure of the coolant.