Why do you
need to do this though? I went into BBI at 40, up until killing the
, but stopped because I assumed things were about to get harder and I wanted to finish up the main story before going in due to the major upgrades I'd be getting.
During post-game, I killed Ur once, soley for the daggers, then farmed Everfall for approximately four hours, grabbing everything I needed for myself, as well as some good upgrades for my fighter. I stepped back in BBI at 55 (finished the game at 50, but Everfall forced those levels) and it's been a breeze for the most part, after learning an enemy's weakness. You get enough random non upgrades in BBI anyway that sell for tons of cash, and you can't take two steps without gaining a level.
He's practically the same level that I was at that point.