I think an addendum would be fine. But be careful, the admin people must see tons of explanations for why they're applying for PT so they should be pretty good at sniffing out BS. Also, check to see what % of students are PT. If it's high, they may be more forgiving since they're obviously looking to fill all those slots. I don't think your PS or addendum will matter that much in the end, though. I'm convinced it's all about the numbers and they just make us write this stuff to make it seem like they care about the whole application.
"You're like bear, with these claws, and you're thinking how am I gonna kill the bunny. You're poking at it and thinking how am I gonna get in PT."