Bourbon could be made kosher, and even kosher lepesach with the following critera:
a)a corn only mash,
b)acceptance that corn is not chameshes haminim, (obvious) and
c)corn, being native to the Americas, is not kitniyos either (not so obvious, nor well accepted)
d)the malting agent and yeast are chometz free.
This is not really rocket science, and could be done in the home bathtub, kitchen and garage, given some know how, and a sense of what can be put into dual-use. And also a new charred oak barrel, likely the most elusive and expensive of the must haves.