While initializing an LSP client, how to set ProcessId in InitializeParams

While initializing an LSP client, is there a way to set InitializeParams.ProcessId?
This code:

        public async Task Initialize(CancellationToken token)
        {
            var @params = new InitializeParams {
                Trace = _trace,
                ClientInfo = _clientInfo,
                Capabilities = _clientCapabilities,
                RootUri = _rootUri!,
                RootPath = _rootUri?.GetFileSystemPath() ?? string.Empty,
                WorkspaceFolders = new Container<WorkspaceFolder>(WorkspaceFoldersManager.CurrentWorkspaceFolders),
                InitializationOptions = _initializationOptions!
            };

Doesn't seem to include ProcessId from anywhere.
Some servers require ProcessId to be set, so I came up with the following workaround:

        options.OnInitialize(OnInitialize);
        //...

        private Task OnInitialize(ILanguageClient client, InitializeParams request, CancellationToken cancellationToken)
        {
            request.GetType().GetProperty("ProcessId").SetValue(request, (long)System.Diagnostics.Process.GetCurrentProcess().Id);
            return Task.CompletedTask;
        }

Is there a proper way to accomplish this?

Start with the Initialize method and its InitializeParams construction shown in the issue, then trace how the LSP client sends that request. Check how the OnInitialize callback is applied and whether ProcessId has a supported configuration path. Done means the client can set ProcessId without reflection and the value reaches servers that require it.