Getting the bases loaded is more of a challenge then the actual homerun. Often times you’ll get a double or triple which breaks things up.
On Rookie difficulty though, the CPU tends to have terrible fielding. Therefore, you can bunt the bases loaded. Stick your bat out but don’t swing in order to bunt. The CPU may catch a few but you should be able to get three on base this way. When loaded, raise your hands to call for a pinch hitter. The pinch hitter provides a homerun off the bench. You just have to make good contact.