At this point, that is unfortunately not possible via the API.
You can of course pull either all (.GetEntries()) or open (.GetOpenEntries()) entries from a debtor, and then generate a PDF yourself
The statement of account PDFs that can be generated in the e-conomic web application are really 'reports' - supporting a wide range of filtering and other options, e.g. date interval, whether to generate a full statement or open entries only, etc..
As such, exposing this in the API would probably need some way of specifying which entries to include.
We generally don't like to expose functionality 'mimicking' report filters exactly - but prefer allowing integrators to supply the exact data to be included. I.e., for a debtor statement of account, the logical thing would be to allow generating one while specifying exactly which entries from the debtor should be included.
In any case - any further input from both yourself and anyone else who might be interested in this functionality is highly appreciated; since that will allow us to (1) Get an idea of how important this is, compared to other requests, and (2) Make it sufficiently flexible and accessible that as many as possible may benefit from it.