Here's my new idea to accomplish this: have a member of the team that is batting throw the pitches to his teammates. Various players can do this even those not playing the field. There are no balls and strikes. The batter must swing. If the batter misses, that's a strikeout. If hit foul, the batter gets another pitch. Base runners would not be permitted to take leads.
The pitcher would not field. The defensive team would still have nine players and the offensive pitcher would be like the umpires, part of the field.