You could plausibly fit a piece of plastic pipe into the pipe as an inner sleeve but not a good idea, wouldn't be able to get it to seal properly for one and it's just not right. To repair a cast iron downpipe you need to cut the broken section out and fit a flex rubber connector in or replace the whole shebang.
I wouldn't be putting any sort of a joint inside the wall. (If it leaks you may not realise until it's too late!) Replace the section through the wall complete.
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