Sorry FrenzyHuman, no can do.
Tried it myself a while ago and I also went here in hope of finding some info but they all said the same as I'm telling you now:
The bombardment range is fixed to 1 no matter what you enter in the .txt files. Maybe you could do something in SLIC (just guessing) like:
-create an artillery unit on a square next to target.
-use it to bombard nearby square.
-kill the newly created unit.
I don't know how that will work in general (AI?) but let
me know if you try it.