There is some capability for this in both MultiPing and Ping Plotter. If you enter your target like this: My Host Name

Then "My Host Name" will be used for displaying that on the graphs in both Ping Plotter and MultiPing.

Will that work for you, or do you need something a bit more? There is no way to edit this IP -> Name association without restarting the trace (and reentering the IP and Name), but this might be just what you're looking for.