Thomas and his players signed a giant 20m x 12m 'Make Britain Proud' which is touring the country to rally support for the bid 24 hours before details of London's plans are revealed for the first time.
Welsh Olympic bronze medal swimmer David Davies, relay gold medallist Darren Campbell and Wales coach Mike Ruddock also showed their support for the bid by adding their names to the giant flag.
They are the latest celebrities to sign up as the UK's biggest and brightest stars in the worlds of sport, politics, art, fashion, music and entertainment demonstrate their backing for the London 2012 Olympic bid.
Kelly Holmes, Amir Khan, Sir Alex Ferguson, Dermot O'Leary, Cherie Blair, Roger Moore, Joseph Fiennes, Matthew Pinsent, Lord Coe, Samantha Bond, Craig Doyle and a host of Coronation Street stars have already signed up.
On Saturday Welsh rugby legends JJ Williams, JPR Williams and Gareth Davies will also show their support in a special appearance at the Millennium Stadium for the clash with New Zealand.
To Make Britain proud and back the bid simply visit: www.london2012.org/en/support/register/ or text LONDON to 82012.