WPF: template or UserControl with 2 (or more!) ContentPresenters to present content in 'slots'

I am developing LOB application, where I will need multiple dialog windows (and displaying everything in one window is not an option/makes no sense).

I would like to have a user control for my window that would define some styling, etc., and would have several slots where content could be inserted - for example, a modal dialog window's template would have a slot for content, and for buttons (so that user can then provide a content and set of buttons with bound ICommands).

I would like to have something like this (but this doesn't work):

UserControl xaml:

<UserControl x:Class="TkMVVMContainersSample.Services.Common.GUI.DialogControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Background="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"
    >
    <DockPanel>
        <DockPanel 
            LastChildFill="False" 
            HorizontalAlignment="Stretch" 
            DockPanel.Dock="Bottom">
            <ContentPresenter ContentSource="{Binding Buttons}"/>
        </DockPanel>
        <Border 
            Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"
            Padding="8"
            >
            <ContentPresenter ContentSource="{Binding Controls}"/>
        </Border>
    </DockPanel>
</UserControl>

Is something like this possible? How should I tell VS that my control exposes two content placeholders so that I can use it like this?

<Window ... DataContext="MyViewModel">

    <gui:DialogControl>
        <gui:DialogControl.Controls>
            <!-- My dialog content - grid with textboxes etc... 
            inherits the Window's DC - DialogControl just passes it through -->
        </gui:DialogControl.Controls>
        <gui:DialogControl.Buttons>