What is the ruling on exchanging the Sudanese pound for the Saudi riyal on a deferred basis?

The Shaykh : All right, ten Saudi riyals for fifty pounds, that is the price in the market. So a person who needs Sudanese pounds comes and says, “Give me forty for ten, not fifty.” Is that permissible or not? It is permissible, because usury of excess in a like-for-like exchange does not apply in the case of these currencies. But if he says, “Give me fifty for ten,” with a delay in taking possession, that is not permissible, because usury of deferment applies to these currencies. The evidence that it is not permissible is the saying of the Prophet (peace and blessings be upon him): On this basis, we say to the brother who sold Saudi currency for Sudanese currency that it is obligatory for them to exchange possession.
Okay, if the state prevents the export of that, is it possible, for example, for him to give Saudi riyals now and transfer them to a bank there, and when the transfer reaches the beneficiary, he agrees with the bank to buy Sudanese pounds equivalent to the amount there? Some people say, "I do not know." They say this is also not possible. If it is not possible, then out of dire necessity, we say: there is nothing wrong with delivering Saudi dirhams and taking Sudanese pounds in exchange there out of dire necessity.