I was at the suppliers and they had a plastic screed which you could put onto an extendable pole which they wanted $60 dollars for.
So I figured I would build my own.
A few stops later I had acquired a nice piece of 22.5 degree angled pvc, 7 feet long, cost $7, and a shop broom with a 3 foot sweep, plastic not wood, cost $10.
I cut off the bristles from the broom and screwed on the pvc strip with 4 panhead screws, which I had cut down to 3.5 feet.
It is pvc so it will not damage the wires, (unless you do something really abrupt) and it is shaped nicely so it moves the puddle of SLC around and can also give a trowel finish depending on how you hold it.
I used the broom handle as I was doing a 400 sq ft kitchen, but you could unscrew it and install an extendable painters pole for a bigger job, or even screw on a bigger blade as well.
The wires themselves act as a depth gauge, but if I have to do a level jogb without wires I could easily attach a pair of adjustable runners onto either side for a couple bucks extra.
I will post a pic later on when I get some time.