Ok, this works, with the licensing caveat that Sergey mentioned...

oform = CREATEOBJECT("form")
oform.ADDOBJECT("ComReader","ComReader")
oform.ADDOBJECT("test","cntTest1")
EVENTHANDLER(oform.ComReader.OBJECT, oform.test)
oform.show()
READ EVENTS

*!* definition of cntTest1:
DEFINE CLASS cntTest1 AS CUSTOM
  IMPLEMENTS DMSCommEvents IN "MSCommLib.MSComm"
  PROCEDURE DMSCommEvents_OnComm() AS VOID;
      HELPSTRING "Occurs whenever the value of the CommEvent property changes."
    * add user code here
    ?oform.Comreader.INPUT
  ENDPROC
ENDDEFINE

You need the form reference.