[Clamsoda]

You're going to have a very hard time finding help with XML. Relying heavily on XML is discouraged for various reasons, and there is only one thing XML can do that pure LUA cannot: creating secure templates.

You could give your frame an OnClick script, that checks for the button, and toggle frame locking that way.

local frame = CreateFrame("Button", MyReallyNeatFrameName, UIParent)
 
frame:RegisterForClicks("AnyUp")
frame:SetScript("OnClick", function(self, button, ...)
    if (button == "RightButton" or "MiddleButton") then
        -- Execute whatever method you'd choose for locking your frame.
    end
end)