This sounds like something a third party browser or Safari plugin could easily add in... assuming third party browsers are allowed to do PIP at all. Just have a little script add or remove whatever attribute from the video that's there if you're premium and not if you're not... or am I crazy to assume this can be done solely from the client side?
	
		
			
		
		
	
				
			 
 
		 
					
				 
						
					 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		