rospy has an allow_headerless option that uses the time of message arrival according to http://wiki.ros.org/message_filters#ApproximateTime_Policy, but I suspect you want C++ to handle lidar data.

Ideally you could modify the publishers of the floats to use marti_common_msgs/Float64Stamped or similarly stamped messages, or you would introduce intervening nodes that listen to the regular std_msgs Floats and then republish them with headers with the current time. You may want to add a rosparam or better yet dynamic reconfigure param to subtract a little time from arrival time as a manual tuning mechanism, though that is hacky and brittle if you change your system and more or less latency is introduced, otherwise put the conversion nodes as close to the originator of the float data as possible (on the same computer).