Thanks all... it seems, as generally always, within the capability of the average home garage.
As mentioned Trig, I've left the polishing shop to extract them... but I do like your idea of the expansion bolt - never thought of the one. As for the hacksaw idea... wow, assumed a hard shell + wondered about how to get full depth to the cut, let alone the careful patience required...
I have a Seadoo jet boat whose plastic impeller wear rings you (bloody regularly) remove this way... over the years the old hack saw has invariably, um 'marked', the casings. Boat... don't care... but Honda!!!