I think the only way is to look at the source code of cport library (which is in pasacl) and try to understand / modify why it only triggers the OnError event after a bunch of bytes have been received.
remember that windows cant handle received charecters in real time, it is usually busy doing other things and if u make your byte comes every 10 msec or so(slow baud rate) you get a better chance of onRxChar event triggered every 1 byte.

Mahmood