> Thus, learning Mandarin by reading requires first memorizing hundreds or thousands of words, before you can even know where one word ends and the next word begins.

That's not been my experience at all: As long as the content I'm reading is at the right level, I've been able to learn to segment as my vocabulary has grown, and there's always only a few new words that I haven't learned how to recognize in-context yet. Having a good built-in dictionary wherever you're reading (e.g., a Chrome plugin, or Pleco, or whatever) has been helpful here.

My fear would be that the longer you put off learning to segment in your head, the harder it will be.

My advice for this would be that you present the text as you'd normally see it (e.g., no segmentation), but add aids to help learners see or understand the segmentation. At very least you could have the dictionary pop-up be on the level of the full segmentation, rather than individual characters; and you could consider having it so that as you mouse over a character, it draws a little line under / border around the characters in the same segment. That could allow you to give your brain the little hint it needs to "see" the words segmented "in situ".