OLE server contacting OLE client?

I have an OLE automation server application which performs operations
which involves RS232 communication. This means that the response to a
request may come minutes after the request is made.

I would like the client to be free to do other stuff while the server is
carrying out the requested operation. Is there some whay that the server
may contact the client or do I have to create a waiting thread in the
client?
/Kjell-Olov