Thanks for the replies, everybody.
I had looked at size comparisons between .22lr and .25acp and initially thought the two were very close, but upon looking again I do see that .22lr is longer overall.
What I was thinking about was a replacement barrel in the correct size, a replacement firing pin that strikes at an offset, and replacement extractor that's reshaped to fit the .22lr rim.
The more I think about it, the more it sounds like it would be a pretty hairy conversion. I'll probably just enjoy it in the original .25 elephant caliber