Austin Filiere (MIT, D3) was invited to be a fill in player in the Cape League until players returned from the CWS. He lit up the league. He ended up being drafted in the 8th round a couple of years later. Previous to then Cape League he had played in the Futures League, a low level collegiate league that allows graduating high school seniors.
Filiere left baseball after two decent low and high A seasons. Chances are as an MIT grad T Rowe Price offered him a lot of money to leave baseball.