Currently it's possible to add a 0 value transaction on a bank account using the web interface by clicking "New Transaction" selecting "spend money" then adding a positive sum to one account and a negative sum to another account.

When attempting this with the API you get a validation error "The Total for this document must be greater than zero".

This is a simple request to remove the additional validation on the API to allow this transaction to be added (like you can in the web interface).

Something similar can be achieved with a manual journal, however these don't support multiple currencies which means this method can't be used.