First, you need VPS or dedicated Apache server that you have root access. Then create symbolic links to point to one core. (You still need multiple MySQL DBs.)
Sometime, the shared server may let you do so if you have a SSH access.
This information is as of May 21, 2014.
1. Create /concrete/ & /updates/ folder where you save your concrete5 core files
In /concrete/ folder, you save all files under /concrete/ folder In /updates/ folder, you will save the new version of concrete5.
Make sure to set the permission that all of concrete5 can read these core files.
If it's apache server you may want to run the following.
cd [WHERE CONCRETE5 SINGLE CORE FILE]
sudo chown -R apache:apache concrete updates
Or you may just have to change the permission to 775 or 777.
2. Make two symbolic links from concrete5 site
Create symbolic link You need to login via SSH. Then type the following
ln -s [FULL SERVER PATH TO YOUR CONCRETE5's CONCRETE CORE] concrete
ln -s [FULL SERVER PATH TO YOUR CONCRETE5's UPDATES CORE] updates
Again, you need to be careful with your ownership and permission setting of the server. You may not be able to do the automatic download due to the file ownership and permission; you have to manually upload the update files onto /update/ folder.
3. Add server path of central /concrete/ & /updates/ to each vhost.conf
Then, you need to set the following to ALL of your concrete5 site's virtual host config file.
vhost.conf format
Click here for the actual code https://gist.github.com/katzueno/735a5ac6ab4db17bb2c3#file-vhost-conf
EXAMPLE of vhost.conf
If the example above is hard to read... here is an example.
- concrete5 single core location: /var/www/concrete5/
- Site domain: EXAMPLE.COM
- Site location: /var/www/vhost/EXAMPLE.COM/httpdocs
Click here for the actual config https://gist.github.com/katzueno/735a5ac6ab4db17bb2c3#file-vhost-example-conf
Example
Here are my actual sites that running on a single core as mentioned above.
They are running on MediaTemple's VSP hosting plan.
Good luck.