You could dilate with a fragment shader, it would be similar to a convolution kernel with the character in a texture and the shader performing multiple taps in all directions to test for a hit against the glyph, the displacement of the texture tap could be variable under user control and be clamped to the glyph bounds so you don’t hit other glyphs in the image. You could also draw the character displaced up down left right etc in the border color then finally draw it in the fill color in the middle, primitive but effective.
There are other ways using geometry but it depends on how your glyphs are represented in memory in the first place.