Is it permissible to buy something and put it in place of stolen money, or to deduct a debt in exchange for overtime hours, due to the inability to return the stolen amount?

It is not permissible to take money unjustly, whether through theft, usurpation, or transgression. It must be returned to its rightful owners, as Allah Almighty says: (And do not consume your property among yourselves in falsehood). In the event of fear of exposure, one must devise a way to deliver it to its owners. As for additional work, if it was agreed that there would be no financial compensation, then it is not permissible to take money. However, if payment was agreed upon and not fulfilled, it is permissible to take from their money an amount equal to the prior right, and this is known as the issue of al-Zafar (taking what is rightfully yours).