Spool file from oracle database for microsoft EXCEL

ISSUE:
Business user would like to view reports generated from database through microsoft EXCEL. So tab-separated txt file with xls as file extension name is used to generate reports automatically. However, some cell is displayed in anticipated format like 1.2E+12 (12345678912)or 123456789198000000000 (123456789198,12345567788)

CAUSE:
EXCEL does auto-convert for number from tab-separated text files.

SOLUTION:
I didn't find the way to turn off this auto-convert function to save the number as stored text.

WORKAROUND:
You can add something, which is tolerated by end user, to avoid auto-convert. For example, add a comma ',' at the end of the column from query.

Reference:
http://office.microsoft.com/en-us/excel-help/three-ways-to-convert-numbers-to-text-HA001136619.aspx
http://office.microsoft.com/en-us/excel-help/format-numbers-as-text-HP001216512.aspx