The easiest way to do this without modifying the distance sensor drivers or message file is through mavlink offboard messages: obstacle distance rangefinders
The other limitation is that if you want some form of collision prevention, it can only be done currently via multicopter position control. If you need another flight mode, such as mission, obstacle avoidance might be worth a look but it has not been updated in a while: obstacle avoidance
However, both of these methods require offboard compute. You could modify a lot of the code like Alex mentioned, if you need FMU to manage the distance sensors