You can just experiment with how it sounds bring out some bricks and or large books and make a pile of those or garden concrete slabs. ? Experiment how it impacts the sound before committing to a permanent solution.
There are many sellers on Etsy who do something like this upon customer request.My KEFs are still not back (6 weeks) from repair, still I am eyeing this idea.
This is what I came up with for long term elevation after attempts with placeholders will turn out nice:
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Good 'ole epoxy resin with wood, the stuff you use to make thos pretty tables nowadays. Since I have an epoxy resin table already I thought "why not?" since it's the ideal match for the aluminium/walnut KEF Reference 3 Meta and since these blocks will probably outlive me, price might be justified (no price offer yet, still waiting for quote from my woodworker)