Excluding Directories by Modify Date with lftp mirror

So I'm trying writing a little syncing script with lftp and I ran into a bit of a snag I can't seem to figure out.

Basically, I want to use lftp's mirror command ot sync files/folders, but only after a specified date. Unfortunately, the built in parameter --newer-than=TIME only seems to apply to files themselves, as it will still copy the entire directory tree, and just leave them empty, despite the fact that the folders are older than the specified time in the newer-than parameter.

Is there any way to use the lftp mirror command to exclude not only files by modify date, but directories as well?

Thanks in advanced for the information.