After so much research and trial and errors finally i got it to work. When I asked this question I wanted to display 3d model over marker dynamically by downloading it from remote server on SD card and then render it. you could do it using Rajawali api like this
getCurrentScene().removeChild(myCurrentObj);
ObjParser parser = new ObjParser(this, 'mydir\myfile.obj');
parser.parse();
getCurrentScene().addChild(parser.getParsedObject());