Fuck me, I did it! Tried vacuum and dibbles and in the end just repeatedly jabbing it made it appear from the right hole!
At one point it came out of the front derailleur hole in the bottom bracket, and on the chain stay actually popped out of a tiny drainage hole.
Lesson learnt.
Two methods I've used with varying success:
Bent metal clothes hanger through the hole to hook the cable
Thread tied onto the cable and hoover up to the hole