To answer my own question, I just used the int[] blit instead:
int i = 0;
for (int y = 0; y < textMap.getHeight(); y++)
for (int x = 0; x < textMap.getWidth(); x++)
array[i++] = textMap.getPixel(x, y);
buffer.blit(array, textMap.getWidth(), textMap.getHeight(), 0, 0, 80, 100, textMap.getWidth(), textMap.getHeight(), false);