Hi, I had the exact same problem with my estate version. Ford recognise the problem on the focus but not the mondeo yet. Bit the bullet and bought the new switch from the dealer for about £30. Perfect ever since. It all operates off a tiny microswitch under the rubber you push to open the boot.
Hope this helps!
Exactly as you said. Disconected the connector coming from the external switch and boot no longer opens when it feels like it!
Also got functionality back on the cabin switch too, billy bonus.