That's correct. You could buy the refundable ticket now, wait for your 241 voucher to be issued (no more than a couple of days) and then refund the flight in this month/year. That way you probably wouldn't even have to come up with the £2k in the interim if it's all within one billing period.

However, I wouldn't be altogether sure that the 241 voucher would stay valid, so it's the risk you'd have to run.