Sure: 
 
package Extensions;
import com.tinkerforge.*;
import com.tinkerforge.IPConnection.TimeoutException;
public class DualRelay extends BrickletDualRelay 
{
public DualRelay(String uid)
{
	super(uid);
}
public void switchState(int relay) throws TimeoutException
{
	boolean relay1 = getState().relay1;
	boolean relay2 = getState().relay2;
	if(relay == 0)
	{
		if (relay1)
		{
			setState(false, relay2);
		} else {
			setState(true, relay2);
		}
	} else if(relay == 1)
	{
		if(relay2)
		{
			setState(relay1, false);
		} else {
			setState(relay1, true);
		}
	}
}
}
     
I've made a git repository for the extensions at Bitbucket.org: 
https://bitbucket.org/Antonas/tinkerforge-extensions   
If any of you want an invite, send me a PM.