So do you guys think if I get something like an 88a wheel I'd be able to hold my brake for several minutes without the wheel getting slick and having the brake stop working?
Dude, come on, common sense says if you constantly scrape a piece of metal against something that's softer than it, it's going to wear down, along with all that repeated friction making both materials hot and slick. Wear shitty shoes. If you need to be holding your brake for several minutes, you don't need to be hillbombing. Either grow balls and use the brake intermittently, wear the shoes, or both.