Hey, I have the perfect solution for you!
Don’t.
See how easily that works? You’ll be treating them just like you did prior to the existence of Facebook. You might have to mail them a card at Christmas, or give them a call when Aunt Myrtle is in the hospital to tell them you think of them.
For me, it was a difficult choice, but ultimate most of what my distant relatives were posting were cat memes or political diatribes (myself included). We weren’t using it to keep in touch, just amuse (or annoy) each other in different ways. I’ve only missed it once, and that was because I needed to get a letter of recommendation from a college instructor and she has almost no other online presence I can find.