I'm a "beginning" composer (not very good yet, but I know basic theory), and an orchestral song I'm writing will require modulation from Bb minor to a "related" major--in this case, Bb or Eb. I have almost a solid two minutes of music in Bb minor already, and I'd like the final modulation to Bb major to sound somewhat surprising. The problem is that I have no idea what key(s) to modulate to (if any) for the B section and beyond before the final modulation.
This is similar to the 'Tierce de Picardie', where a piece is in minor until the last cadence, where the sun comes out with a parallel major chord to finish. Generally, it's going to be a perfect cadence - listeners are going to expect the final tonic minor - so in your case, an F or F dominant seventh harmony leading straight to Bb major will suffice.