Unfortunately, Osmosis won't work here. You have 2 options.
1) You can run your line around the walkway. If you do, you'll need to calculate the Transformer Wattage to figure in the line-loss due to the excessive length of the wiring. The higher the wattage, remember, the more that heat is generated. So if your transformer is in a room that's hot to begin with, you'll get that much more heat. (Mine is in the basement which is unheated / uncooled.)
2) You can tunnel under the walkway. You'll need to dig out each side of the walkway to get down deep enough to do the digging from BOTH sides. You're not going to be able to do the job from just one side of the walkway. (You arms aren't long enough!) WHen you finish tunneling, run your wire through a 1/2" piece of piping. What I did was 'bow' the piping a little (arched it), and layed it under the walkway so the arched-part is HIGHER than the ends. This way, water won't run into the pipe. YOu can perforate the pipe on your own along one side and set the pipe into the ground with the holes facing down. Then, backfill. Lay in some sand/gravel first, then the pipe, then some more sand and gravel. Pack it as you add a little at a time.
There is a 3rd option and that's to knock out one section of the walkway, then lay your pipe, then re-concrete the section. I have another tip. I soldered my connections. I didn't use those 'clamp kits' that come with the light sets. Since you, basically, bury the lines, the connections tend to come loose over time. Also, I put some Bathroom Caulk on the connections, wrapped them in electrical tape, then shrink-wrapped them up. Do leave some slack all along your 'run' because the ground does move. If there's some loose line in the ground, you'll reduce the chances that your line will 'break' due to ground movement. Oh, and make sure you get the properly rated wire for the LENGTH of your run!
My best to ya and hope this helps.
PS: I have Kichler lights. They're metal; not plastic.