That gave Callender the chance to take a good look at plenty of promising talent, such as flanker Jorja Aiono, in what was another disappointing campaign which ended with the Wooden Spoon.
Callender will provide some experience in a youthful squad against the Baa-Baas as Lynn and his coaches look towards the autumn WXV Global Series and beyond.
“It will be a mixed squad this weekend and that’s so exciting for the future,” said Callender.
“Having that development pathway will be good for strength in depth, which we have lacked in some positions over the years.
“It’s going to be a great occasion. I’ve played at Twickenham once before with Harlequins and it’s a great stadium to play at.
“It’s a massive opportunity for us to showcase what we have been working on as a new group with lots of young players.”
Wales have a break after the Baa-Baas game before WXV fixtures against South Africa and USA in September then two October Tests in Japan.