Why don't Cas give Boyle a slighty improved deal and send him out on loan to Salford, abit like what Saints have done with scot moore. There are a few players out on loan while they develop like McNally at his hometown club whitehaven while being on Hudds books.
simples
p.s i do want ryan to stay at Cas but if he isn't going to get the game time , a loan move seems best imho rather than lose a home grown forever.