1) your board wont allow you to terminate a big contract like that if there are more than say 6 months left on it (even less)
2) try and make him happy/willing to sign a new contract, then offer him less and less duration (that normally does not work)
3) offer him out, someone will eventually bite!
4) offer to loan him out at 50% of his wages with £0 transfer fee, if someone accepts at least you are recovering 35k per month, do this until his contract expires...