Looking for some info on modifying the shape of seat bolsters please!

Basically I have a bora ST with black seats which I quite like, but the distance between the bolsters is a little wide for me, so I tend to sit with my hips against the right hand one and my ribs against the left hand one, which makes my back sore on long journeys. Would a retrimmer be able to add half an inch of foam to the inside faces of the bolsters inside the existing fabric cover to create a snugger fit?

Cheers