I've updated the OtlComm.pas unit in OTL home page with a lock-free circular buffer, donnated by a fellow Slovenian Delphi programmer who goes by a nick 'GJ'.
This code is doubly-work-in-progress! I haven't even test it. It is disabled by default and you have to define conditional symbol LockFreeBuffer to use it.
If you'll be making any comparisons to my original communication code and especially if you find any problem with new code, let me know.
UPDATE: I decided to use OTL_LockFreeBuffer instead of LockFreeBuffer. Repository has been updated, too.