Cheers for this, will get crayons out! I think this is what a blind puller does, but expensive/not sure lbs will have - and not sure any would reach down the 80mm or so needed...Not done this but I thought of using a tool similar to a headset cup remover.
Get a length of steel tube that will fit inside shim, cut 4 slots in it like headset tool, splay out then fit to end of length of rod so that splayed out end is facing up. Maybe if you can fit nut to other end of rod so you can put sliding weight on rod to make slide hammer.
Use in similar way to removing headset cups, push down past shim and pull upwards on rod, using it like a slide hammer probably best.
Aye, mine's the factory fit 29.6>26.4 alloy one. Could have left it in for evermore - but want to transplant my 27.2 dropper in there. Because I'm super rad/gnar and all that, see.Mine looked/looks plastic so left it in place when I was polishing the frame