"could NEVER be duplicated outside"
It would be possible to print a PGP-type text at the bottom of each receipt, that would not be possible to generate outside the machine. It would be different for each receipt, but by court order could be de-encryted back to a known text verifying that it was an original from that machine at that time. There are many ways to secure electronic voting in the future that would eliminate dead and duplicate voters and other comman frauds. Of course, the examples of bribery you cited might remain.
could be de-encryted back to a known text
Good idea. Very expensive to do a verification, but a good idea.
If we are to give reciepts, why not just abandon the concept of a secret vote? Like the Iowa Caucus, where you vote by standing with other supporters.
A ballot where you actually sign it, and maybe smear your thumbprint on the ballot too.