Hmm ... not sure you have to do all of that ... if you find the post on your masto instance you should be able to just boost that.
Otherwise, yes, there is a painfully lacking degree of interop. From what I've gathered, mastodon needs to do better at representing group based structures. Lemmy/kbin federate just fine, but masto can't represent and manage the content in any way that is useful, which is hampering the growth of the fedi IMO.