Again I was mislead by the name of a property
oTextLine.TextLineType = Constants.FV_TEXTLINE_CENTER;
I thought that this would be useful to center the text within a given space. But I could not find how to use it.
I found a straight-forward method:
Towards the end of my function I have inserted (aLenght is the space width):
textLen = oTextLine.Width;
boundLeft = (aLength*CM - textLen)/2;
oTextLine.BasePointX = x0*CM + boundLeft;