When I did this recently I also realised there are pre-drilled holes alongside the single socket. I decided to NOT use these in the end. Rather than replace the single with a double (or triple), I added a new double spaced away from the existing single.
Colin is right about Clearcut Conversions. Excellent. And they seem to be the only reseller I could find online who sell the trims to match the current style of CBE products used in the Eriba.
There are great instructions from Clearcut, but they suggest a 54mm hole saw. Depending on which sockets/switches you're fitting you may not need such a large hole. I used a 30mm hole saw for the USB and single switches I fitted. Less chance of breakout that would be visible!!