Hey Don, Installing an IEC into the C11 would be messy and difficult job. Even with a empty chassis that you can wash out with soapy water, the IEC is a tough job to do well with hand tools. If it is a steel chassis you need to cut through then just forget it. Dangling an IEC on the outside is a clever solution, but the IEC must be rated for that use, I've not seen any like that.
Hardwiring the upgrade PC is your best idea, imo. An IEC, being a temporary connection, would increase the source impedance of the mains power, so there is a good technical reason to avoid adding an IEC connection.
Make sure that you have grommet protection and an excellent cable restraint on the new hardwired cable. You might have to improvise since it will be a thicker cable.