After a little trial and error I found that using a sharp point to puncture the tyre (from the outside) in exactly the place I wanted the spike to come out, allowed me to just push the sharp end of the screw threw the tyre from the inside, the end result was a nice uniform double row of carbon steel zinc plated spikes, threaded into the chunky rubber part with no hope of being pulled out.
The screws stick through the rubber on these tyres about 10mm which if I am being honest is about 5 more than I really wanted but without buying chunkier tyres or shorter screws that's not going to change.... and I like the slightly excessive look.
At this point I started being paranoid about pushing a screw back into the tyre and shredding a perfectly good inner tube whilst riding.
So I coated every screw head with strong flexible glue and then glued an old inner tube over the glued screw heads. I can also guarantee that the good inner tube isn't stuck to the glue when it is time to change it again.
This whole process took just under two hours per tyre to fit two rows of 50 screws in each, this lined up with the tread pattern and as I am not heading anywhere remotely uneven I decided the outer edges of the tyre were best left un-spiked and if the grip wasn't good enough I could always spike the central row of tread too.
I decided to inflate the experimental tyres to 40psi as this was the lowest manufacturer recommended setting so if the spikes needed to flex a little they could without ripping the rubber blocks apart.