As far as I'm aware of, no Visibility of layer constructor does not allow this. In the siemens-game-api the visibility of layer constructor was protected and I used it to subclass Layer, but in sun's implementation this is not possible. So sad the only way to subclass a layer is to wright your own implementation of layer and all of the javax.microedition.lcdui.game classes. Luckily you can decompile the WTK jars and take their sourcecode (as did i ) for tiledlayer, sprite, etc. it works fine on my nokia 6630.
Or, you can take source from any other opensource, there are a lot of implementations of gameapi in MIDP1.0. Though the main drawback will be that your api wont work as fast as natively supported one.