Post on fediverse first, then screenshot it and share with other socials saying it's from lemmy or wherever in the headline. Maybe even say which community it's from. And it could be a watermark of some kind too.
The more people are aware of the fediverse communities, the more they might check it out and just leave reddit entirely.
the idea was more, that more people will migrate, when it's obvious that Reddit removes posts with useful information. so people would look directly at the resource - Lemmy.