Unfortunately, it’s not that easy. I guess you would have to exclude the dependency ical4j from ical4android and include a new submodule (= the downloaded local ical4j) instead.
Are there any plans to do this?
We have already done so: https://gitlab.com/fdroid/fdroiddata/merge_requests/1023/diffs
By the way, we’re not related to F-Droid in any way and everybody can submit merge requests to fdroiddata. You can do so yourself, too