The link manager provides approach to add anchors with unique ID and name. The name should be inserted dynamically in a collection shown in the "Existing Anchor" drop down. For some reason this dropdown is never populated without reloading the RadWindow.

Possible resolution is forcing the dialog to reload on each show:

<telerik:RadEditor ID="RadEditor1" runat="server" OnClientCommandExecuted="OnClientCommandExecuted">
</telerik:RadEditor>

<script type="text/javascript">
    function OnClientCommandExecuted(editor, args) {
        var command = args.get_commandName();

        if (command === "LinkManager") {
            var dialogOpener = editor.get_dialogOpener();
            var linkManager = dialogOpener._dialogContainers[command];
            linkManager.add_show(function () {
                linkManager.reload();
            });
        }
    }
</script>