The best thing you could do, but is probably not practical, would be to open up the ground with a cultivator or sidedness rig. With that much manure applied there should be plenty of N still there. The saturated soil has forced all the oxygen out of the root zone and by opening it up will get oxygen back in and allow the bacteria to start mineralizing the N again.

A controlled release nitrogen product will do no good because without oxygen the plant is unable to take up much of any nutrients. Oxygen is your limiting factor.