Or, you could just donate to the admins of the instance. They make it pretty easy in general. This is almost as bad as the “I wanna add ads to Lemmy to help admins cover costs” person. Just donate, and remind others to donate if they can.
Edit: I thought about it further. adding rewards would morph the comment section to a popularity contest a la Snoozerville. On top of that, any instance adding rewards would likely be targeted for defederation by others. I didn’t come here for capitalism, thats basically the root cause of the migration in the first place. And again, all of this is easily solved by donating to the instance admins.