There's not really any other way - there is no way for anyone to unstake ETH right now (and there's not even a certain timeline for when people can get their money back!) - that's not a kraken limitation, it's a problem (feature?) of ethereum.
Kraken can't pretend to unstake customers' ETH and stop paying rewards because they have no way of returning the underlying coins to them.
They can just pay the customers and keep what is stuck as their own asset. From what I understand, kraken can stake their own assets but they can not stake assets for others.
True, but at the moment the funds are locked until next month when Ethereum has a network upgrade (Shanghai). If they credited users ETH directly now, they may not have enough liquid ETH on the books if everyone were to withdraw before the upgrade which would remove all trust in the exchange.
They might not have the extra money. If (let's suppose) customers have sent 1 million ETH to Kraken that's now staked, Kraken would need another million ETH just laying around in order to do this.
For something like this you can definitely get a loan or not? They have the ETH, it is just locked up and out of all the coins it is the second least likely to go to Zero tomorrow.
Kraken can't pretend to unstake customers' ETH and stop paying rewards because they have no way of returning the underlying coins to them.