I wouldn't go that far. What I meant is more that Element would've been willing to share our private source tree for Element Android 1.2.2 with F-Droid several days in advance of disclosure, if it meant that they could pre-build the binaries and have them ready to ship the moment that the source was made public.
(After verifying that the public source is identical to the privately shared copy, of course.)
Do you need a full source tree for this ? IIRC major Linux distros do this via preliminary disclosure to a private mailing list possibly with a patch attached.
That way distros can do a local build to verify the patch works and fixes the issue & they then apply the patch in their public infra right after the embargo runs out.
(After verifying that the public source is identical to the privately shared copy, of course.)