Custom VTK objects on server-side only

When running a pvserver with external plugins, these plugins do not need to be loaded on the client, and everything will work as expected, as long as they only produce standard VTK objects.

However, if a plugin creates a custom VTK object as output, on the client-side I get the error

vtkSMDataTypeDomain: Unable to create instance of class ‘MyCustomObject’.

In my use-case, these objects only carry some intermediate results (and are later converted to standard VTK objects by other filters), and do not need to exist on the client-side.

Is there any workaround for this, that does not involve loading the plugin on the client-side?

No, but you may be able to work around this using a Factory on the server side.
It allows you to replace an existing class by one of your own.
See : VTK/Common/Core/Testing/Cxx/TestObjectFactory.cxx

Of course, you could always not expose the intermediate output and collapse multiples filters into one.