To keep the DDS within your monthly limit, you can list for the first flight only and then if you miss out can either:
a. having been placed on standby, get the ground staff to move your booking for you and immediately place you on standby for the next flight
, or
b. use the re-list function on TRIPS to select your next preferred flight, and then pair up the previous ticket reference against your new flight (without any additional DDS being processed). Press SAVE and Halas!
Good luck,
The G.