Maybe I have incorrectly understood what did you mean and in fact you are asking about limiting overall number of impressions per day, not views by the same user. If yes, you just don't understand how are auction-based ads working! Completion speed (number of impressions per day) depends from CPM bid, therefore to get less impressions just pay cheaper price!
I do understand how are auction-based ads work.
The problem is when all other ads expire.
Yesterday I got 28.7k impressions (87% of total impressions). This way my ads will expire all in the same day, and I don't want this.
It would be nice if we could edit active ads.