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It sounds like multiplexing may help. From the description on the wiki

mux is a ROS node that subscribes to a set of incoming topics and republishes incoming data from one of them to another topic, i.e., it's a multiplexer that switches an output among 1 of N inputs. Services are offered to switch among input topics, and to add and delete input topics. At startup, the first input topic on the command line is selected.

To use it with rosrun:

rosrun topic_tools <outopic> <intopic1> [intopic2...] [standard ROS arguments]

and to use it with roslaunch see #q84386.