The simplest solution would be to reboot the Siberian Republic [1] as a Chinese suzerainty. Ideally after Putin dies as part of a deal to the new ascender. Maybe together with giving them personal co-ownership in some major ventures there.
> East because they are blockaded at sea currently, if they would invade Taiwan
Siberia and Outer Mongolia remain closer and thus cheaper and more-secure sources than anything coming in over ocean, which in essence means from Australia, South America or Africa.
Russia is recently bluffing a bit there, Putin had a visit for the first time recently, I think it's China related:
https://en.wikipedia.org/wiki/Kuril_Islands_dispute
China is already owning the area with investments and a lot of workers/projects there are already Chinese. Seems like Russia already lost control ( unofficially)