It is very annoying. I have mine setup as a wifi access point only (I use pfsense on a server as a router). There should be a way to stop it searching for a connection when you want to use it in this way.
Apart from removing the relay, which would invalidate any guarantee, there is nothing you can do, as its not intended to be used in this manner. As its only on loan from BT, you cannot start modifying it. The relay controls the switching of the digital voice circuitry, whether you use DV or not.
The solution is to use a proper wireless access point.