Answering adequately your question would at least require an
understanding of the reasons for the limitation you seek. If the
limitation has a legal origin, some solutions may not be legally
acceptable, while they would be if it is simply a decision based on
some metaphysical belief or choice of yours.
The book distributor (publisher or reseller) is unlikely to accept a
complicated scheme, for practical implementation reasons, and because
costomers might react negatively to unpredictable availability
... though they apparently tolerate a lot of aggravation.
One thing your distributor might accept is to keep for himself
whatever income is in excess of your set limit.
Another possibility is to set up a small company that manages your
books, and deals with the publisher or the retailers. For exemple,
you could decide to be your own publisher. Some indie authors do that,
I believe. Then your company can make arbitrary profit, but you, as
its manager, will decide each month how much you deserve. But I would
do some checking to make sure that such a setup is legal wherever you
live.
