Only way you could really do it is to cut straight lines down inside and then 'peel' the sections away with a hammer and chisel. Would need to be really careful though as the cast can be brittle.
If it's a run Lead joint, get some heat into it, might soften the lead enough to dig it out and release the spigot section left. Then either a plastic to cast adapter or the DC-1 as linked above.
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