Stubborn Team Mate! NEED HELP PLEASE!

My friends and I have made a ranked team, but havn't even tried one match, because we have a top laner who won't put effort into it. We try to practice, but he either doesn't play, or won't play. Currently, we have a few team comps we want to try, but unlike everyone else, he wont adjust. He will only play rengar top, which he only won once, because of an AFK on the enemy team. He knows Lulu, but won't try her. Claims that rengar is the best. I wouldn't mind him practicing and trying to get better, if it weren't for the fact that his previous role (which is now mine) was support. He played it for 6 months, and at this point owns mostly support champions, but never got better at the role. He never pokes, helps ADC, or wards. He just sits behind ADC and watches. He never got better, so we all switched roles, but it took a month of convincing for me to get support, because he didn't want to try any other role. He has now attempted every role multiple times, but with only a few champions, because he will not attempt anyone else. He is top now, and it is not working. He is a dear friend of ours, and we would hate to lose him over a game, but we all really want to try for at least gold for our team. My team is at the point of kicking him, but I am holding them back. I need help and I need it fast. Thank you for reading, and I hope you have some advice for me. My friend posted more detail in another thread. Click here for it