restict format replace in a cell
 

Hi All,
I am facing one problem. I am creating a excel file in c# and applying
formats for columns. User will get the excel file from the site and enters
values and uploads again. When user copy and paste the data from some other
excel sheet, the format of the cell are overriden by the other cell formats.
But i want to user to allow to copy only contents not format, even though he
paste the data on to the excel file. Please suggest some way how can i put
this restriction through excel objel model? Please not that i am generating
this excel file on fly in c#.
This is urgent .
Thanks & regards
Anjan