Site for compost bins

I'd like to move my compost bins (Dalek type *2) around the side of the house, but there is only about 1 foot of soil there, the rest would be on concrete. Is there a good way to manage to get the worms in but not have the compost seeping onto the concrete? The base options I see are usually for the full bin, rather than just about half of it.
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To be doubly sure I usually add a spadeful of 'cooking' compost (which is usually full of worms) when I have between 6 and 12" of material in a 'new' bin.