I'm also writing middle grade fiction and dealing with the same issue. I have decided to go with your option #3: use a milder alternative. Though in a different way from how you've laid it out. As such, this is a slight frame challenge in that I'm not directly answering "how to use a swear word indirectly" but talking about how I'm approaching the same problem.
For this age range (approximately 8-12), it's common for books to be read out loud, especially at the younger end of this. Sometimes the child reads it out loud. This is the prime age for the fabulous Read to a Dog program or a child might read a section out loud in class or to a parent. Sometimes adults (parents, teachers, etc) read to kids. If you have word placeholders that can't really be pronounced in full, it gets confusing.
Words like frak and fork work on television and they've invaded the culture (I'm partial to frak myself), but they're linked with specific TV shows (Battlestar Galactica and The Good Place) which will date them badly in a few years, even if the words are still understandable in context. They also can sound a lot like the original, which is problematic when read out loud.
Also, children on the younger end of middle grade are learning about swear words and still getting the hang of them. They are more about shock value than meaning. If you use a placeholder (including standard downgrades like shoot or heck as well as made-up words) that basically only means the profane word, then that's the reference they're getting out of it. You might want that but, as an adult, what you're getting from it is different from what an 8 year old is getting from it. Ask your daughter and her friends what they think.
I decided to use words that are not profanity and are things that age group use and understand, but are not very nice. Basically mean words that hurt. Something that even an 8 year old will feel in the gut.
I'm still working out the full range, but so far, I've got words (both nouns and adjectives) such as:
I also use sarcasm, mocking, and put downs like "if you're in charge, we're doomed." This isn't the same as swearing because it's more thought-out and less explosive, but it sets up a character as nasty and the reader can easily imagine her/him as the type of person who would swear in other circumstances. Not all people who swear are mean of course, so this only helps in some cases.
middle-gradeto tag my question. I think if there is a tag that starts with
you-it would show up to people as the type in the tag field while they're looking for