I think you can follow below method:
- Prepare new VMs for new 4.2 installation.
- Get 'setup.properties.last' from existing 4.1
- Install ( just run deb package ) 4.2 in new machine.
- Collect 'setup.properties.last' from 4.1 and run setup.py with that.
- Complete installation.
- Check new server's oxAuth login ( it will be admin login only ).
- If all went good till now...
- Run Cache Refresh to pull user's information from 4.1
- Manually migrate all OpenID clients from 4.1 to 4.2.