As far as I can tell, you can't do it conveniently. That is, git-rebase does not give you an option to preserve the committer date. Unless you give the --ignore-date (or its alias, --reset-author-date) option, it will always preserve the author date. However, there is no way to make git-rebase preserve the committer date, unless some manual script is crafted.
The best you can do is to make the committer date equal to the author date. Recently (in 2020 Q4), git-rebase --interactive has gained the ability to use the --committer-date-is-author-date flag with the interactive rebase. Before that, there was no way of influencing the committer date at all with the interactive rebase. Note that this flag does not preserve the committer date. It merely makes the committer date equal to the author date.
You might be thinking "well, isn't that effectively preserving the committer date, since normally the committer date is always equal to the author date?". Normally, you would be correct. However, there