The 36-year-old left Cardiff Blues for fellow Welsh side the Crusaders and hasn't played international rugby since winning his 100th Test cap in the 2007 World Cup.
The 2005 Grand Slam winner is currently recovering from groin surgery but is hopeful he will return to action when Wales begin their preparations for the defence of their European crown this autumn.
And if Thomas does manage to regain his fitness in time for the start of the tournament, he will follow the likes of fellow Lions Scott Quinnell, Jason Robinson, John Bentley and his hero Allan Bateman in representing his country in both the 13 and 15-man versions of the sport.
"For me it's fantastic. I never thought that I'd put on the Welsh jersey again, especially not a league jersey," said Thomas, who has been selected in Iestyn Harris' squad for two October friendlies before tournament games against Scotland, Ireland and France.
"To me, probably one of the biggest things is that my idol in rugby growing up - and even to this day - has been Allan Bateman.
"And to follow in his footsteps, the fact that he played dual-code international; when you get to emulate what your hero has done in rugby almost makes you... well I couldn't really have asked for anything more from my rugby career."