Cannot override private static method using EMC

Here's an example of a simple test, in which the return type of a Private Static Method within a Class is needed to return a String different from what it would normally return:

void testCheckSunrise(){
    WeatherMonitor.metaClass.static.findSunriseTime = {-> '5:57 AM'}
    WeatherMonitor testSubject = new WeatherMonitor()	
    assertEquals('5:57 AM', testSubject.sunrise)
}

And here is the Class itself:

public class WeatherMonitor {
    def getSunrise(){
        findSunriseTime()
    }

    private static findSunriseTime(){
        '7:15 AM'
    }
}

The result of the test execution is always '7:15 AM' and so the test will always fail. This would be a great help in Unit Testing techniques, especially Test Driven Development in Groovy.

It would be great to see Groovy have this capability.