Space between words in Kotoeri Japanese input method

I would like to specify that a space between two Japanese characters in Kotoeri (Word 2008) appears in half-width instead of full-width. (I.e., I don't want the spaces to be the same width as the characters; I want it to look more like the space between words in an English text.) How do I do that? I went to Kotoeri Preferences > Character, but the only choice is to change the width between numerals, not between regular characters. Thank you for your help.