When I first read the title of this post, my immediate thought was "You can't. T-ball is boring!"
When studying early childhood education, there is an emphasis on understanding the attention span of the children you are teaching, and ensuring that your lesson plans consider that attention span. For kindergarteners, it is often said that you can't plan a lesson that lasts longer than about 5 minutes, without building in some sort of change--whether it be the opportunity for the children to stand up and sit back down, or do some sort of movement, or perform some activity individually, etc.
If you think about the nature of T-ball, it is set up completely opposite to this concept. You basically have one kid active at a time, with all of the other children on both teams completely passive. And in my experience, it is not unusual for each child's "at bat" to last at least five minutes.
When you think about the game this way, the question that comes to my mind is "Why are any 5-year-olds succeeding at T-ball in the first place?"
I think a better choice for small ones is a game that allows them to be moving all the time--soccer seemed to work well for both of my kids.
Even with a game like soccer though, working too hard to get the children to understand things like hustle, or the benefits of hard work, or anything like that is asking them to get something that they may still not be able to understand developmentally. This understanding of development is inherent in the reason for short lesson plans--the brain of the average child at this age is simply unable to remain focused on a single concept for longer than about 5-6 minutes. I found that understanding early childhood development was invaluable for reduced frustration as my kids were growing up (and continues to be so, even though they are now 19 and 20).
Cooperative play is a developmental skill that children are still just learning about at age 5. You can find lots of information about it on-line, but most will echo this website which states "Cooperative play is where play finally becomes organized into groups and teamwork is seen...Cooperative play begins in the late preschool period, between the ages of 4 and 6. It is uncommon to see children reach this stage until these later years, as it requires an evolved set of organizational skills and a higher degree of social maturity."
Keep in mind, too, that these ages shown are averages--individual kids hit each stage at their own pace, and the timing has nothing whatsoever to do with their intelligence or their future success in life. Your son may be a little bit slower to hit this developmental stage than the other kids on his T-ball team--or maybe he is just more fierce than they are about not doing something that makes no sense to him.
I found sports in general to be a fun way to track the developmental changes in my children. When my kids were playing soccer at 4 or 5, all of the kids would be bunched around the ball, chasing it wherever it was on the field. The only exception would be the goalie, and most of the time s/he was examining bugs in the grass, or chasing a butterfly, or something. If I try and imagine what my kids enjoyed about the game at that age, I think it was probably something along the lines of "Wow, I am a good runner. I am glad I can run as fast as all of these other people. Oh, cool, I kicked a ball and didn't fall."
As your kids get older, you will see the team begin to spread out on the field. Sure, they are getting better at the sport, but they also have a much better grasp on the concept of cooperation--because developmentally their brains are now ready to process information in this way.
Anyway, this a very long-winded way to say--nothing is likely to drive a parent nuts more quickly than trying to get your child to understand a concept that his/her brain simply can not understand yet. Consider yourself lucky that your kid enjoys the time he spends in the dugout (I spent years with both of my kids arguing that they had to stay in the dugout until the game was finished, and couldn't leave and go get a popsicle). If you are really lucky, you will get to have the experience that one family had during my kid's T-ball years--their child hit the ball, and then while rounding the bases, the kid stopped and gave a hug to every single person sitting on the first bench of the bleachers--no matter whether they were a parent from our team or from the opposing team. That kid knew how to make sports fun!