We attempted the same in July...sorry to say its not going to happen.We met one guy who managed it but he was indonesian..."ride for Peace" charity on a rather flash BM.Dont get excited ..the only way he could get through was with a letter from the Chinese Ministry of foreign affairs and it had taken 2 yrs.The standard way seems to be to apply to the chinese consulate. they will need a concise itinery and will furnish you with a guide..$100 - $500 per day. The problem seems to be you need someone to negotiate with all the petty politicians to allow you to cross their provinces.
We took a pot shot at Boten in N Laos and without a valid visa to China they wont even give you a glimpse....(as for the bike..no way!!!)
All I can suggest is just to hold out. The olympics bode well for opening of the borders to private transport. WE have previously travelled in China by bus and the roads are good. The highway in Laos to the Chinese border was the newest dual carriage way we'd seen and so I am sure it will happen ...just not yet!
We are interested if theres more positive feed back