Go into Retro mode, select your opponent as any Double-A team, choose to be one of the All-Star teams. Set your opponent as the home team. Choose a hitter friendly ballpark like the Astros' Minute Maid Park. Move any better power hitters into the starting lineup. Set hitting difficulty to beginner. Purposely strikeout your first 9 batters. Then, starting in the 4th inning, swing for the fences. If you still didn't hit a homerun the second time through the order, then it is probably quickest to restart.
Note: An inside the park homerun does not appear to unlock this trophy. I tried getting this trophy at the same time as "First, let me catch my breath", and only "First, let me catch my breath" unlocked.