Soran was the one who came up with the camera when he suggested "Let's give Mr LaForge his sight back' when Lursa and B'Etor complained they couldn't take out the Enterprise.
Really it's just more sloppy writing. There was really no point to kidnapping Geordi beyond it would make a convenient plot point later on. He interrogates Geordi about trilithium but that makes no sense either... he already has the sun destroying rockets.
Keeping him hostage as a bargaining chip makes no sense being at the time there was no reasonable way to assume that Picard could figure out where they where. Heck kidnapping a Starfleet officer would increase the chances of them being followed. It's just as likely they might write the incident off if Soran beamed back alone. They certainly weren't in any hurry to go after the Romulans that attacked Amargosa to begin with.
The only purposes kidnapping and torturing Geordi serve is to remind us Soran is the bad guy(just in case we hadn't figured that out yet) and to conveniently hand him back with a spycam in his VISOR to let the old Bird of Prey stand a chance.