I've experimented with very conservative correction doses near bedtime. If I have dinner at 6 pm and my sugars are still high (through mistake, snacking, or otherwise) around 4 hours later when the insulin's finished, I'll take a very small dose - 1 or 2 units - and it'll drop my numbers by a few points to get me some peace of mind.
For example, even just last night I had a 12.0 reading after some fresh fruit, and I was able to bring it down overnight to a more acceptable 8.5 for morning. I don't know if it went lower and then came back up, because I didn't wake myself to test halfway through.
In my personal case (meaning, this probably won't apply to you) 1 unit with no food will drop me around 2-3 mmol.
I can only do this safely because my basal is at a perfect spot where it keeps my levels steady overnight, rather than going down.
EDIT: Narrowly avoided another one. I was 14.5 from some stew that had a lot of potato in it, took 7U alongside some toast, and within 2 hours I was down to 5.3 . I knew it'd go down further still so I had some cookies.