Ok, so the converter is capable of 1W output (200uA), drawing 100mA unloaded & 250mA fully loaded. That means a resistor divider won't affect efficiency very much.
Since 1100V is 1/3rd of 3300V the number of resistors has to be dividable by 3, and since each (1/2W) resistor can tolerate 500V you have to use at least 7, hence 9.
If we choose to run the converter at as much as 1/10th power it'll draw 115mA and output 20uA at 3300V. R=3300V/20uA=165Mohm (/9=18Mohm each).
A 20uA divider current related to 0.3uA electrode current is a factor of 67, ensuring a voltage stability of 1.5% (16.5V) on the 1100V.
Choosing 33Mohm instead will reduce the divider current to 11uA, giving a stability factor of 37 (2.7%, or 30V).
Now, I don't know how big an engine you're going to make, but I saw a figure of one drawing up to 300nA, which I used as a basis for my calcul-/ estim- ations.
But I came to think; will you be using the converter & 4300V for driving something else besides? If so it won't be quite as easy as this, but it'll still be within reach.