When you do your find and replace in Word, instead of replacing all spaces with a period or quote, replace them with this:
The catch is that you can't use Preview as you normally would. Your post will look correct the first time you preview it, but once you preview, the converted HTML will reappear in the post form, so if you hit Preview again, or Post, the spaces you added will be wiped out.
So the workaround is:
1) Write your post in Word, then replace the spaces with the code above.
2) Copy the post into the DU post window.
3) Hit preview -- if it looks good, RE-PASTE from your Word document back into the DU post window and hit Post, not Preview.
Otherwise, make any necessary adjustments in Word and then re-paste again -- but if you always re-paste from Word before previewing or posting it should work. Bear in mind that if you need to edit the post, the same thing applies -- when you go to the Edit page, the spaces will have been converted again. So make sure you keep the Word doc until you're sure the post is good and you don't need to edit it.
Hope that helps...
Edited to add: lol, I made the preview mistake myself and the code didn't appear correctly, trying again...