Can I reverse my heating zone?
If the radiation is finned tube and you can access the piping from below, you could break-up or split that run in half by running another supply or return connected to the near middle of the run and/or add finned tube radiation in the colder rooms. If you are going to redesign the heating system why not zone some or all the system. You need to answer a few questions such as how the radiation is piped (single loop, mono-flow, etc). There is a lot of possible fixes depending upon just how the system is presently installed. Let us know and add pictures if you can.