Packet length is varying

Dear all,
If the length of the packets coming from an application is varying , But
the most of them are 70 bytes & the app sends the packets in bursts not
continuously.
I use ofdm tx & ofdm rx & 2 usrps to send and receive the packets by
another app.
So if I write 70 in the packet length parameter & if the packet coming
is
less than 70 bytes then it is buffered and not transmitted until it is
70
bytes when another coming data completes it. And so the last packet is
not
transmitted if it is less than 70 bytes as no coming packets after it.
How to solve this problem ? Is there any blocks that can check if the
packet length is less than 70 bytes , it pads it with zeros until the
packet is 70 ?
Or is there any other solutions?
Thanks.