Roguebook

The game saves after you trigger a tower so the best bet is to speedrun the first Chapter for the 2 towers over and over. You start out with an ink (your ink Embellishments should be maxed) then fight the battle on the road to the boss for your second ink. Usually this is enough to reach both towers with the brushes and will take around 3-4 minutes in this case.
If you uncover a Golden Faerie from the first tower then you have to fight it before you can use your inks/brushes again but you can just keep hitting to end the 5 turns and he'll fly away.
If your starting ink or battle ink was the red explosive one that expands the brush radius then you might need to fight a second battle for another ink but usually you can just inch your way over with the remaining brushes though.

This method works for getting the remaining percentage points needed for opening the 1000 magic vaults achievement as well while you're at it.