While not exactly like what you are after the following may be of some assistance too.
Its tested and works well but not consistantly as expected.

Code:

---

 function fade_tree()
{
	my.scale_x=8;//just my scale values here
	my.scale_y=8;
	my.scale_z=8;
	
	while(1)
	{
		my.transparent = on;
		my.passable = on;

			if(vec_dist(player.x, my.x) < 3000)
			{
			
			my.alpha -= 2*time_step;
			if (my.scale_x > 3)//more of my scaling stuff
		{
			my.scale_x += 0.5 * time;
			my.scale_y = my.scale_x;
			my.scale_z = my.scale_x;
		}
			}
			
			if(vec_dist(player.x, my.x) > 3000)
			{
				
				if(my.alpha < 99)
				{
				
				my.alpha += 2*time_step;
				
	
				if (my.scale_x > 8)//same ol same old
				{
					my.scale_x =8;
					my.scale_y = my.scale_x;
					my.scale_z = my.scale_x;
				}
				}
				if(my.alpha > 90)
				{
					my.transparent = off;
				}
				
			} 

		
		
		wait(1);
	}
}

action world_tree
{
	
	my.polygon = on;
	plant_object();// saves manual placement by leaving in the air
	fade_tree();
  
    
} 

---