Maybe, but you have to consider the fact that even if the horses could be trained, the men of the elite cav would be:

1. Fairly indespensible, so no one but an idiot is going to throw them away attacking pike head on.

2. Influnetial nobles/minor royalty, in other words, the rest of the nobility is not going to be pleased with a general who threw away their fathers?
/sons/brothers by attacking a pike line from the front.

Therefore, pike would be effeictivley immune to cav for the simple reason that very few generals would be prepared to try throwing elite cav head on at pikemen, maybe if somebody was actualy crazy eniugh to try such a tactic it would work, indeed, I rahter suspect it would, albeit with appaling causlaties on both sides, but it would at least disrupt/demorilize the enemy pike sufficently for your own inf to try and break the line. The disadvantage is of coures that you now have no cav, and if the enemy pike can just hold together whilst the enemy cav reacts, then your pretty screwed without your own cav to hold the flanks.