http://www.weq4u.co.uk/
I've just been told about this mobile app.
You can work it from landlines too, but it's easier if you have the app.
Once you are in a phone queue you enter 9* and hang up.
When it finally connects to an operators phone it rings you back.
And you don't get charged for the time on hold.
Haven't tried it yet but the friend who told me about it says he's been using it for months and it works like a charm.
(There again he's not rung the DWP, but from what they say you should be able to do it once you have entered the options and got to Vivaldi).