You don't have to implement anything to use a pattern. UI Automation does this for you (acting as a proxy for the target application). This is well explained in official documentation here: Get Supported UI Automation Control Patterns

Here is an example extract:

    SelectionItemPattern pattern;
    try
    {
        pattern = yourAutomationElement.GetCurrentPattern(SelectionItemPattern.Pattern) as SelectionItemPattern;
    }
    catch (InvalidOperationException ex)
    {
        Console.WriteLine(ex.Message);  // Most likely "Pattern not supported." 
        return;
    }
    pattern.Select();