Another option is you can submitt the sales and purchase annexures
one by one party.
Ex : If customer xyz purchased goods 4 times in a month, you can treat as one entry (the total 4 invoice should be added and sent is as single entry.

Annexure I - Vat Purchase
Monthly returnes>form I > annexure I

Annexure II (Vat sales)
Monthly returns> Form I > Annexure II
Download annexure IA latest excel sheet