Undoubtedly, you can increase the size of your ejaculations through diet and exercise, but ultimately, those are marginal improvements at best. You're not going to go out and do kegels and suddenly start spurting a small lake, it just doesn't happen.
If they did, I seriously doubt:
A. This conversation would be taking place.
B. Anyone would consider Peter North as having an above average load, because we'd all be able to do it.
Yes, not ejaculating for a while will increase the volume of the load, but there is a limit, as in, when the testicles receive the signal that the ideal amount of sperm is ready. That varies from person to person, strictly due to genetics. The average male ejaculation ranges from 2 to 6 mL, meaning having Peter North like ejaculations is rare, because he's just genetically different. (I sound like Brucie from GTA IV).
Kegals has no role in increasing seminal volume. It is used to strengthen the reflex necessary to produce consistent back pressure during ejaculation. You can produce as much semen as possible but without consistently high back pressure it will just drop out of the end of your cock during ejaculation and it's not going to look like much. The stronger more conditioned your PC muscle is the higher and more sustained the back pressure will be during ejaculation. That is as simple a concept in my mind as the notion that strenghthening your chest, shoulder and tricep muscles allows you to bench press more weight.
Your seminal volume is a product of signals sent (through hormones) by the pituitary and hypothalamus glands to the testes and the amount of zinc stored in the prostate. It is a fact that the prostate secretes 500-1000 times the zinc that is in the bloodstream. Supplementing with combinations of zinc, magnesium and potassium as well as being sufficiently hydrated WILL increase your seminal output. You say minimal, I know different.
It's not an indictment against a demonstrated theory that many if not most people lack the discipline or knowledge necessary to change a physiological condition with themselves. I work out regularly and maintain a diet with supplementation conducive to that lifestyle. Naturally I'm going to look different from most people who don't or won't. Because they don't or won't that doesn't dispel the reality that a proper regimen of diet and exercise is determinative in a person's fat to muscle ratio.
You're right in the sense that a man is not going to simply swallow a pill and magically start spurting jizz like a fire hydrant..no more than a man would be able to take a pill to change his body type from fat to fit. It's a matter of consistently conditioning your body for the physiological change and unless you have the knowledge and discipline to consistently maintain a regimen with both you shouldn't expect desired results with either.