I guess my point was that you can't with just a straight file copy. This definitely needs another program, and these programs will do exactly the same; copy it and then set the date modified back, you just don't notice as they do it in the background. @jlewis can either use something other than file copy (e.g. your robocopy suggestion thanks @craig hart, or one of the many other tools out there like fastcopy, teracopy etc.), or if there is some reason he's trying to automate his process specifically with copy then he'll have to do what those programs do, copy and then revert the timestamp.
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