I agree with commonsensical.
I have used R pace workouts in the precomp phase with my athletes for several years. Don't worry about limiting the rest. Take as much rest as needed to run the subsequent workbout at the same pace as the previous one. These workouts are important to develop the muscle strength and coordination to efficiently run at race pace.
There is some anaerobic component to these workouts to be sure, but training the anaerobic system is not the focus. It's similar to doing long hill repeats. In fact, because our track is snow covered most of the winter, we often do hill repeats at R "effort" on days Daniels calls for 400R in the precomp phase.
You didn't say how old you were, but if you're an adult that normally races 5k and up I think you will find R pace (which is normally 1500m pace) to feel hard. On the other hand if you're a high school student who races 800/1500 in the winter/spring and the 5k just in the fall, I think you will find R pace to be quite "doable" with sufficient rest.
As your body learns to fire the different muscle groups efficiently, I think you will find these R pace workouts to get easier as well. Don't start running them faster when this happens. Either cut the rest a but or just enjoy the fact that you're getting better and psychologically get ready for the much more intense workouts to come in the next phase.