Tom Varndell got Wasps' final try, the Dragons ending the game on the attack.
Varndell notched the third Wasps try after a good period of pressure, Walder's conversion again wayward.
Flanker Michael Lipman and full-back Nick Abendanon replace Lewis Moody and Tom Varndell in the squad.
Varndell was happy with his performance but delighted with the overall display of the Saxons team.
The scoreboard see-sawed in the first half after Tom Varndell scored inside five minutes.
Tom Varndell's second-half effort sealed the bonus point with Dan Hipkiss and Louis Deacon also scoring tries.
Prolific Leicester wing Tom Varndell is one of five nominees for the Land Rover Discovery of the Season award.
BBC: SPORT | Rugby Union | English | Catt nominated for players award
Varndell, who has four England caps, would appear a ready-made replacement for Voyce.
Tom Varndell then went over to give Wasps a five-point lead at half-time.
The Tigers stole the final Premiership play-off spot from Quins when winger Tom Varndell scored in the 77th minute.
"I had my opportunity a couple of years ago and failed miserably back then, " Varndell told BBC Radio 5 Live.
Australian centre Kefu, 29, arrives from Castres Olympique, number eight Ward-Smith, 31, from Bristol and 23-year-old wing Varndell from Leicester.
Ugo Monye and Gonzalo Camacho scored tries while Varndell crossed twice to give Wasps a 16-15 lead at the break.
Andy Goode touched down for the first of his 19 points on five minutes before Tom Varndell's try 10 minutes later.
It was Walder's deft chip over the top that Varndell gathered to score on 33 minutes but his conversion drifted wide.
The game was settled six minutes from time when Irish turned the ball over and Jacobs broke clear to send Varndell in unchallenged.
The Premiership match was level at 10-10 after 30 minutes with Varndell's brace cancelling out Michael Claassens' try and five points from Ryan Davis.
Loffreda was boosted by the return of England backs Dan Hipkiss and Varndell, along with second row Marco Wentzel and tight-head prop Martin Castrogiovanni.
Toby Flood replaces Charlie Hodgson at fly-half, Jamie Noon partners Mike Tindall at centre while Mathew Tait and Tom Varndell come into the back three.
Johnson had to request permisson to replace winger Varndell with Abendanon.
But tries from Steve Kefu and Tom Varndell, and two Walder penalties, won it for Wasps, with Paulica Ion's late effort for the Exiles mere consolation.
The visitors hit back with four tries before the break via Matt Smith, Ben Youngs, Billy Twelvetrees and Tom Croft - Varndell claiming another in reply.
Varndell's second, from a neat inside pass by Walder, then pulled the scores even again at 18-18 after the stand-off added a brilliant conversion from distance.
Haughton, who had replaced Varndell at half time, gathered the ball to score before Walder added the conversion to seal a memorable win for the Londoners.
Bath's Nick Abendanon was also drafted into the squad in place of Tom Varndell, who is short of match practice after falling out of favour at Leicester.
Although the visitors did score through Danny Care and Varndell, tries from Ma'a Nonu, Sione Lauaki and Jimmy Cowan sealed a comprehensive series victory for New Zealand.
Varndell opened the scoring when Jeremy Staunton's drop-out kick fell straight to him in space and he seared away from the covering tacklers to cross in the corner.
Murphy also converted his own try before being replaced and Vesty took over the kicking duties when he converted a brilliant try from Tom Varndell which Johne Murphy created.
Wasps responded with a debut try from Varndell, who started the move with a 50m break and then finished it after a darting run and delayed pass from Danny Cipriani.
Also looking to catch the eye of England coach Martin Johnson will be Leicester Tigers trio Tom Varndell, Harry Ellis and Jordan Crane, along with Bath's versatile back Nick Abendanon.
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