"This is a one-off," insisted the 2005 RBS 6 Nations championship-winning Wales coach who quit the national job during this year's tournament.
Ruddock's last visit to Twickenham, in February, saw Wales crash to a 47-13 defeat by England.
It was the last time he was in charge of his country in an away game. Ruddock departed after the following week's 28-18 win over Scotland in Cardiff.
But he is adamant he is not seeking any form of revenge over England.
"I'm just happy to be involved with a tremendous group of players and I'm looking forward to a great game of rugby," he said.
Ruddock's involvement with the Barbarians was arranged before he started his new job with Welsh-based recruitment company Acorn and he said: "My employers have been good enough to give me a month off to fulfil my commitments."
He maintains he is currently "very happy" with his new life outside rugby.
"I've been in the game full-time for 20 years and it's good to have a break.
"I'm enjoying the weekends off. I went to the FA Cup final at the Millennium Stadium and I've been over to Italy a couple of times to watch my sons play there," said Ruddock, who accepts it is inevitable that his name will crop up whenever a high-profile coaching vacancy arises.
He admitted there was an approach from Guinness Premiership club Saracens "a couple of months ago" but he ruled that out for family reasons.
"My kids are doing their A and O-Levels and I didn't want to uproot them at this time," said Ruddock, who was also contacted by Welsh club Llanelli Scarlets after Gareth Jenkins left them to take the Wales job.
"Llanelli spoke to me but it didn't go any further than that," he said.
Ruddock denied there has been an approach from Bath, who have just lost Brian Ashton to England, but he said: "It's amazing how these things get out of hand so quickly.
"I suppose I'm bound to be linked with that one as it's not too far from Wales.
"Even before Brian left, a broadcaster phoned me three weeks ago asking if I was joining them as I'd been seen in Bath - but I was never there. I'd been working in Wales for my company all week."