Marking message as imap/seen via filter?

Does anybody know if there is a way to mark messages as seen using the content filter or other functionality within MD?

If not, could the API or command line be used (ie. via "run a program" action of content filter)?

Any pointers will be appreciated.

If there is no simple solution going forward, I will look into external scripts for filtering/process via IMAP.

Thanks,
Alex