The only solution is to scan the handwriting at a much higher resolution. Typically, handwriting may be only 12 points high, which is 1/6th", but to make an acceptable vector outline in FontCreator you need a sample at least 200 pixels high. To use the grey pixels as well as the black ones, you need to adjust the threshold on the image import dialogue.
Please see this tutorial thread: Size Does Matter
To make fonts look better at small sizes on screen, you need to add greyscale values to the font.