I assume you have the "can Grow" property set to true in this text box. I am
also assuming that the textbox is big enough to handle all words in your
table if the lines were to break between them (if not, you either need to
exand the textbox or make the font smaller).

I know of no property that forces line breaks in this situation to always
occur at a blank, so the only solution that comes to my mind is to create a
few extra text fields in your table that are hidden to users, and write some
VBA code that will parse your text field into these hidden fields. You then
would have control over where the breaks occur.

Then, stack these fields in your report column rather than use the original
field. You could automatically run the code each time the report is opened.  
Seems like a bit of work, but that is all that comes to mind.