Thomson played for two months on no wage last season on his return to Easter Road as a free agent.
Fenlon has been delighted by the 28-year-old's progress, after a series of niggling injuries curtailed his progress at Middlesbrough.
"We said last year when Kevin came in that his fitness levels probably weren't where they needed to be," Fenlon said.
"He's had a great pre-season and he's looking very, very sharp at the moment and he'll be a great addition to the squad."
Former Queens Park Rangers striker Vine moves to Hibs from St Johnstone and, like Thomson, has signed a one-year contract.