Accounting for VAT on sales made via Amazon

A client of mine (who is VAT registered) has recently started selling goods via Amazon, with some being subject to VAT and some not (eg childrens clothing & sales abroad). When he sells goods he receives the proceeds, less Amazon's commission, directly into his bank account. No sales invoices are issued by him.

Does anyone else have clients who deal with Amazon? If yes how does one identify and account for the VAT? As far as I am aware Amazon do not produce any reports which would assist with this and he does not want to have to raise invoices for each sale he makes (these tend to be high volume, low value). If all goods were subject to VAT this would be simple as one could calculate the VAT on the net proceeds. However, as he sells goods which are zero rated & exempt I am unsure how the numbers can be easily identified - anyone have any suggestions?