Is there anyway to disable the copy/paste function in a cell in an excel spreadsheet but still be able to edit/type in the same cell?

For example, I want to set up a data entry spreadsheet where a user has to enter the same information twice (example - cell A1 and B1) to stop keying errors, there is a warning message in cell C1 that warns if cells A1 and B1 do not match but i do not want the user to simpily copy and paste the contents of A1 into B1, therefore negating the purpose ok the check column.

Any ideas would be a great help.

Thanks

Sam