After digging around on the forum for a bit, I found the following thread which seems to contain my answer:
There, manu explains how to use "Subtractive merge from this changeset interval", which does what I need. I read about subtractive merge on the blog and on one of the documentation pages, but there the interval option was not mentioned, so I didn't know about it.
After testing it on a dummy repository, I used it on our real repo and it worked great!
PS: Maybe I'm failing at googling and reading the docs, but I still can't find the official documentation where it says that subtractive merge works on an interval, maybe that's something to add.