Try feeding him a bottle and then cuddle him till he is almost asleep. It will take a while for this to work because he has had you wrapped around his little finger for 8 months now. Once he is almost asleep, put him in the bed, sit there and softly talk to him, pat him on the back. Once you have done this a couple of days, stop talking and just pat him on the back for a few minutes and slowly decrease the time you do this. Yes you will spend a few days sitting by the bedside to get him to sleep but after you have him sleeping during the day you will find yourself with so much time it will be worth it. Also start playing a soft cd with lullabies when he is sleeping. As you get him ready for sleep, turn on the cd as a cue that it is sleep time. I always played the radio, cd's or tapes when my kids slept. The advantage of that is you don't have to tiptoe around your house and pray that no one rings the bell and wakes the baby. Get them used to sleeping with everyday noise and they will sleep anywhere. My daugther slept through an ambulance siren outside her window for 5 minutes cause the neighbor had fallen and the guys were stupid enough to not turn off the siren until I asked them to. But she slept right through it at 8 months. I could vaccum, play with the kids I sat for occassionally and she never missed a beat. My sister in law did not believe in my noise desensitization and if you walked down her hallway while the baby was napping she turned the ringer off on the phone, had a sign over the doorbell, and had specific boards marked with tape cause the squeak of the board would wake the baby. I do not have that much time to avoid a board so the baby will sleep. I stayed there for a week and by the time I left that baby was sleeping through jumping in the hallway and the phone. I couldn't get her to sleep through the doorbell but my concession was that it was truly loud(plus it was right by the nursery door) and I didn't think a dead man would sleep through that one.. So we left the sign.
Stay strong, be firm, discipline starts now. He is obviously secure taking naps on you now but he can't be in kindergarten and you have to drop everything to run to the school cause it is rest time and he has to have you there to be the little blue mat. NOW is the time to set up his ability to learn trust. Sit him in the bouncy seat while you work. If you leave the room verbally tell him things like "Mommy is going to put the dish towels she folded in the kitchen, I will be right back" When you return say "see, that didn't take but a minute, you were so patient for mommy" and then rub his cheek or give him a smooch. He will be learning object permanence now and peek a boo is a great thing to start now. put a towel over your face and say "where's the baby" or "where's mommy" then drop it and say "there you are" or "here I am". Before long he will be doing it himself and having a great time. He has to learn about how the world works and you are his primary teacher.
Good luck,
C.