I doubt it is even possible to rap off 550; the thinnest I have ever heard of being used for rappelling is 5MM and it was by an elite high altitude solo aplinist.
No reason why you can't just take a few extra turns around your friction device, beit a figure 8, carabiner or whatever. Just be aware that you'll need extra friction, its strength is marginal, and you're using it for something its not intended for.
On the other hand, a rappel is not something to be set up in a hurry. Ask me about the time I rappelled right off the end of my rope.
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