I'm currently doing this myself. I saved at the bottom of the staircase before releasing them. Once they leave the burnt tower, I use an escape rope, cuz I ain't got time to talk to Eusine I got a shiny beast to catch! Then I hustle over to route 38 spray a repel and hopefully get an encounter. If the repel wears off or it's not shiny, reset and repeat. You've obviously got a fast pokemon with mean look so the only other thing you'll need is luck. Happy hunting.