True random will not be possible, since it will lead to disconnected facilities.
If you want to feel less cheat-y when manually placing you can call an external randomize function (via spreadsheet or other software) to determine where to place a specific facility.
For my games i use a bash script with the code below to provide me the coordinates of the entrance, the rest of the facilities will be placed based on personal preferences.
for i in {1..2}; do echo $(($RANDOM % 6 + 1)); done
Please note that this script is based on the personal preference of defining the upper left spot to be {1,1}, it is not based on any coordinate system used by the game itself.
