Mate has a 185mm shock that needs to be 190mm – could he use 2 offset bushes to LENGTHEN the shock? would it make up the missing 5mm?

Depends on the size of the hole as to how much offset there is (more with 6mm, less with 8mm) but normally 3-6mm offset at each end.

technically you can lengthen like you say, BUT under use they often rotate back to the default position (reducing I2I) unless they are clamped uber-tight.

185mm is an odd size…shock from a Specialized?

from a cove to go on a prophet

really? what Cove came with a 185mm I2I shock, it’s a very unusual size, I’ve only ever seen them on Specializeds

see this thread – http://singletrackworld.com/forum/topic/wtd-fox-rear-air-shock-185mm-for-a-marin-03-tara-frame