If your customers are sending you a list of transactions, you can create your own csv in excel. The headings you'll need are as follows:
1 - Date
2 - Description (Payee included)
3 - Amount in
4 - Amount out
If the transaction is money in, leave money out blank; and visa versa.
You can upload this into the Banking screen, and link it to the account to which you're uploading the treansactions for. This will give you a really easy to use system for adding transactions in through our banking screen. You can even create banking Rules for repeat transactions and ones which occur more often that have the same description as past transactions.