Technically a compression 4 single TIFF should combine to compression 4, is that not the results you are getting (Perhaps you are getting LZH compression)
Have you looked at Cesar's article in September issue of the UT magazine?
http://www.utmag.com/wconnect/wc.dll?9,7,10,,2148

>Does anybody know how to create a multipage tiff in compression 4 (CCITT4) from individual tiffs with compression 4.