I'm not sure what things would "block" it, but perhaps send a signal to do nothing, maybe set display to the current display? Basically try to find something that does nothing, but could prevent it from launching the screensaver.
fe.add_transition_callback( "transition" );function transition( ttype, var, transition_time ){ local redraw_needed = false; if( ttype == Transition.EndLayout && var == FromTo.ScreenSaver ) { ::print( "\n\nSCREENSAVERRRR\n\n" ); //return true; } return false;}