Piece of string definately!
You could build an .xls file which you would have to build up by entering Lat/Lon of each HLS in (in decimals) and then it could work out the distance (as the crow/helicopter flies). It would, as a result, be quite a text heavy file though. Can't be that difficult though... It's all pythagoras at the end of the day!
Most operators use a variation of the string/map and quoting software.