Best wishes on your trip!
A Chinese friend of mine in Beijing did a very similar trip in January 2012, but he rode all the way from Beijing, and also the return (I recall it was a total of 13K kms, but I might be wrong). He went solo, on an 883, although his wife joined him for a small part. I think he went through 4 countries in SE Asia (Thailand, Cambodia, Vietnam, Laos), but I forget. He entered from Yunnan, and returned the same way, if I remember correctly.
This particular trip was featured in Motorcycle magazine, issues 05 and 07, 2012 (all in Chinese). You can often find old issues in bike shops. I could scan the articles and post them here, or email them to you, if you cannot find them. He also posted the ride report on the HOG website, but I can't seem to find it. Sorry. His HOG posts detailed the procedures & documentation, and I seem to recall that it wasn't that difficult.
I can also put you in contact with him. He runs a motorcycle shop (RPMCN) in Beijing. Here is his shop's website:
http://home.51.com/rpmcn
Detail about his trip is on his shop's website (he has posted several of his trips - I think he put something like 60K on his 883).
I think he also has a taobao shop with the same name (RPMCN).
Good luck!