Correct me if I'm mistaken, but it sounds to me like you want to purchase a BUF-CLE-LGA ticket, with the return LGA-CLE-BUF, but you only intent to use the BUF-CLE legs? CO won't allow that to happen.

Anytime you miss a flight, CO will cancel the remaining downline flights in the PNR. I wouldn't waste the money on flying, IMO. It's only a 3 hour drive max from BUF to CLE.