A very easy way to train a spike is with light.
Cytokinins cause internode elongation, which is what mostly causes the spikes to grow. When exposed to light, they are destroyed. On the side that is not recieving light it grows faster. That is why a plant grows toward the light.
So if you want to train a spike:
Put the only source of light the direction you want the spike to grow. The brighter the light (below burning) the more stunted the spike. The lower the light, the more etiolated the spike.