If you go online and search Flexi Drills or Canada Flexi Drills, you'll find some tool companies who sell these products.. What you ( and others too) might want to get is their 72 inch long x 5/8 or 3/4 masonry flexi bit.
Above you are talking about the guy not wanting to put a conduit under the walk... WHY?... imagine if you could get a 6 foot long drill bit and simply bore a small hole under the walk in the gravel/sand below, and pull your wire through very simply?
We do this all the time and it's a huge time saver and with just a hole one one side of the walk and a narrow trench a couple of feet out on the other side, it s a minimally invasive method to cross a narrow walkway.