如何为在IIS共享主机上运行的Joomla配置PHP basedir

I have the following setup:

  • IIS 10 with Plesk Onyx 17.8.11.
  • Joomla 3.8.13/PHP 7.2.10. The website is hosted in shared hosting provider.

After installing Gantry 5 I get the following warning on the Joomla Control Panel page:

SplFileInfo::isFile(): open_basedir restriction in effect. File(gantry-themes:/\beez3) is not within the allowed path(s): (D:/Inetpub/vhosts/xxx\;C:\Windows\Temp)

Looking at the PHP Settings tab of the Joomla System Information page I see the following setting:

Open basedir D:/Inetpub/vhosts/xxx\;C:\Windows\Temp\

As far as I can tell, the D:/Inetpub/vhosts/xxx\ is incorrect since the root folder of the website is:

D:/Inetpub/vhosts/xxx/yyy

In fact, I had to set the Path to Temp Folder to D:/Inetpub/vhosts/xxx/yyy/tmp in the Joomla Global Configuration Server Settings in order to install Gantry using the Joomla Install From Folder method.

On the other hand, I cannot find a way to modify the value of Open basedir setting either from Plesk or otherwise. As a result, the Gantry component page reports the same error:

Twig_Error_Runtime An exception has been thrown during the rendering of a template ("SplFileInfo::isFile(): open_basedir restriction in effect. File(gantry-themes:/\beez3) is not within the allowed path(s): (D:/Inetpub/vhosts/xxx\;C:\Windows\Temp)").

Please note, that I refer to Gantry as an example; The same problem occurs for every other Joomla extension I tried to install.

Is there a way to properly configure Joomla/PHP on my setup?