Try this toolbox for putting back the EXIF info:
http://www.ozhiker.com/electronics/pjmt/
suggesting:
1 - read exif info from the original file.
2 - resize the file
3 - read the header information of the resized file
4 - put the original EXIF into the new header of the resized file
5 - put the modified header information of the resized file back into it.