This feature only support for Windows Server 2008 with DotNetPanel control panel hosted by Exabytes Network.
To run different .Net Framework versions from your application pool, you shall create a virtual directories and assign the mentioned application pool (virtual directories) as different .Net Framework version.
1. Log into the DotNetPanel.
2. Select the hosting package.
3. Select the Website.
4. Click on your domain.
5. Select on the Virtual Directories.
6. Create new Virtual Directories.
7. Select on the virtual directories link.
8. Look for the Extension tab.
9. Change the .Net Framework version and save it.