I don't think it would benefit him in the way he wants to use it.
Think of it this way. You have a nice glass of koolaid all tasty and sweet but you can't drink it. You can only look at it and follow the directions on the box. Then you dump half out and put water in. Now its all diluted and probably tastes like crap. So you add more sugar and more koolaid powder to hopefully get it right, but you never know. Then you have to dilute it again. Rinse. Repeat.
Hmm thats a crappy analogy. What can you expect at 8:30am? I think I need coffee too
All I can think of is what a huge waste of money to have to be constantly dosing zeovit to get those levels just right, only to be dumping it down the drain on a weekly/biweekly basis because you don't have a skimmer.
The zeovit principle is based on constant dosing. It only takes a couple minutes etc but you're dosing daily regardless to keep the system intact. If you're going to disrupt the system by removing half of the dosage through water changes and then dilute it and toss some extra in to hopefully make up for it, I don't really understand how it can be beneficial for your tank in the way its supposed to.
Its not that he can't do it, I just don't think he's going to get the best bang for his buck.