[Discuss-gnuradio] Continuous vs bursty source for fsk_tx.py

[Meenal]

While using fsk_tx.py currently, I use the -R or repeat option to send out 
a continuous stream of packets.  What if I have a bursty source such as 
socket or a named pipe which has data only when the user above the socket 
decides to send it?
How can I mix the "real data" with some "dummy data" , so that the src 
always appears to be continuous or in other words the fsk_tx.py script sees 
an infinite stream of data it needs to process and send out ?

Such a set up would also require that on the receive side the correlator 
needs to intelligently throw out the dummy data and only push the real data 
out to the sink.  Any ideas ?
Thanks,
Meenal