Yes it work's for me.
Stepps: in My Case With One Primary Site Server
1. Install SQL Server on Site Server an give the System Account Permissions
2. SCCM Preinst /stopsite
3.Detach DB an Move DBs and Log Files to SCCM Site SQL
4.Attach DB
5. Perform SSCM Maintenance or Site Reset --> Modify SQL Configuration
6. Test SCCM Server after Restart.
7. When SCCM Working I Started to Upgrade without errors.
After Testing I move back the Database to the Remote SQL Server by step 2-6
I have Testing this by LAB Environment before upgrade the Production Server :
Note: I have no Information that this Way is Supported and no Warranty