To be able to update Buying Price Unit automatically when you change the Buying Unit

We have a customer who uses multiple units of measure. There has been some mistakes made where they have changed the buying unit but not the not Buying Unit Price/ It would be good to have a setting (either Stock Setting or Pop Setting or Product Group and/or Stock item level) where you can say if the unit changes to update the buying price unit automatically. A setting would be good as it wont change anything for those who are happy but can then give you some extra control.