I would try and sell him to one of the leading Championship sides.
How much would they pay him, £20,000/week? If we could get £1m for him but give that to Bent as part of a pay off. That would leave him about £25,000-£30,000/week short of his current salary, or £1.25-£1.5m. We pay him off £1.5m but add a clause in contract that if the club he goes to get promoted, they pay an extra £1.5m transfer fee. This would cost us £1.5m and the loss of any transfer fee, against £3.5m less any loan contribution from another club, with a long shot of getting our money back.
A permanent move might give him more motivation than another loan to get his career back on track, albeit at a lower level.