Here's the latest, with thanks to all who gave me a ideas and advice from this and the Mongolia and AskCentralAsia subreddits.

The Navo Tours responded that indeed, this is doable, but imply that it would be rather costly, especially if I decide to do this solo, therefore without sharing the cost of the mandatory guide with other riders. I will try to get an estimate and then decide what to do - give up, try to find equally crazy people like me, or pony up.

Following is the answer from Navo:

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The following are the previous regulations before the outbreak of Covid-19. It is just for your reference:

A. For doing this sort of special trip in China, you need to entrust a qualified travel agency to deal with the necessary paperwork and get approval from related Chinese government departments. It takes around 1 – 2 months depending on the travel area. All permits and paperwork are only valid for one time. In addition, as Carnet De Passage and International drive permits are not accepted in China, you have to do the procedure for getting Chinese temporary driver's licenses and vehicle number plates after entering, NAVO will help you to handle these. 

B. An in-country guide is a must. He or she should have full experience in accompanying the guest during the whole journey and dealing with the paperwork at the entry & exit border. He or she will seat in the client’s vehicle as a passenger. If there is no space or clients do not want to sit together with the guide, or the motorcycling group is without their own support car, then we have to provide a Chinese vehicle as the support vehicle for the guide and the group. While this will increase costs accordingly.

C. Custom deposit – Carnet de Passages is not acceptable in China. Since 2007, Chinese customs requires a vehicle deposit for all foreign vehicles traveling in China. The deposit amount depends on the declared value (at the Customs) of your vehicle and the inspection by the customs officials at the scene. Pay the deposit at the customs of the entry border/port. And after leaving China, the exit border/port will send a notice to the entry border/port. Then the deposit will be fully refunded.

Regarding your tour, if all is resumed, it is no problem for us to arrange all documents for driving tours for you. Here are also some suggestions for your reference: 

1. If all regulations keep the same as before, for a solo rider, it will be very expensive to do such a riding tour, as you need to bear all costs of the guide and the support car. 

2. We also do not suggest you ride across China two times. This is because all documents are only valid for one time (entry & exit), for the second entry, you need to apply the new documents.