Use separate partition to house icloud sync files

Has anyone had any success using a separate partition on the internal HardDrive of their Mac to house the files that sync to their iCloud? I am asking because I am planning on dual booting to two separate Mac OS when Mojave is released due to the depreciation of 32 bit applications. I plan on using High Sierra to run those 32 bit applications and I don’t need the system to bloat itself with downloading the same files from the iCloud twice but I need to be able to access the same Docs from both OS’s. So having two separate OS’s point to the same partition that houses the files being synced to the iCloud should provide the solution I need… The question here is how would you do this, seeing as from what I understand there may be subtle differences between Mojave and High Sierra and the way the access and store user data.