I can't speak for the clearedDate, but FYI there are discussions in the FpML Regulatory Reporting WG to add more timestamps / add a flexible timestamp structure.
I would refer you to this thread: http://www.fpml.org/_wgmail/_rptwgmail/msg00396.html
If a concrete proposal came out of this it would likely be implemented in a later draft of FpML 5.2. I would suggest you keep checking the mailing list or participate directly in the reporting working group to get the opportunity to shape the design. This may solve the limitation you see with the clearedDate, I am not sure but I thought I'd mention this related discussion.
Apologies for the delay in answering your post.