Here is the context it was used in: "If we close our eyes in a silent room, the feeling of having a body is not something we can imagine away." Does "imagine away mean to imagine something instantly?
The preposition away here has the sense at a distance or removed from the current physical or figurative context, as when we send something away or tell children to put their toys away.
In the construction VERB X away, VERB acts as a causative and the preposition acts as a secondary predicate on its object X: that is, one causes X to be 'away', out of sight or out of mind, by VERBing.
Your sentence, then, may be paraphrased:
. . .the feeling of having a body is not something we can dismiss from consciousness by a mere act of imagination.