It just is not going to work with fonts. The way to do this is to convert the font to curves in your DTP application, then fill the curve with white, and use a black outline.
Outline.png
It is possible to have a pair of fonts, one solid font and one outline font and, in some applications, display the solid font in white and the outline font in black on top of it so that the display appears as if it is a single font even though it is really two fonts used together.
As it happens I have made some fonts with which one can do this. It works quite well when producing pdf documents from a desktop publishing package if the desktop publishing package can support layers.
What application are you using?
You could try using the fonts available from the two following links for a feasibility experiment if you wish.
I have now made the attached graphic using the two fonts mentioned above. I used Serif PagePlus X2 (a desktop publishing package) to make the graphic.
graphic.png
William Overington