I'm just going to venture a guess, but have you tried expanding the column once in Excel so that there's more room for the number?
If the above doesn't work, then there's nothing you can really do except to reformat the column as "text" instead of a number (scientific).
I get upset at Excel that when I export a specific date format (Jan 1, 2009 10:00 am) it will reformat it to 1/1/09 10:00 am instead of showing what I want. No way I can get around that other than to change the format of that particular column.
I wish there was better news, but there isn't. The only other thing you could try, is writing directly to a document written in Excel 2007 XML format. Not sure how feasible that is though.