Correct.. you cannot target him unless he is visible, and the only way to get him visible is to attack.
Yes you can attack your own forcefield (or even attack one of your own conjurations, or something with a Block on it) to make him visible.
When enchanting him though, remember he is a non-living and incorporeal creature... some enchantments are picky about those. Block, Nullify and Retaliate all require a "Corporeal Creature", so the Stalker cant receive them.