This is just speculation on my part but after reading about Caroll and West Ham, I was just thinking about something.
What if we told Real Madrid to put in a loan with an option to buy for 25 million pounds? Madrid knowing how tight our board is would probably think it's a meaningless gesture as we won't pay it.
If Sahin has a monster season for us, we simply cough up the cash and keep him and leave Madrid scratching their heads. If he doesn't perform that well we send him back.