Webi report scheduling to be scheduled using excel based date

Requirement is like user doesn't have fixed holiday for the entire year which keeps on changing month by month. so user want the webi report to be published on every third working day based on custom excel calendar rather than custom CMC based calender. Since they are more comfortable with Excel where they will keep on updating there 3rd Working day monthly and report would be published based on that excel based value. Is it feasible or workaround for this? Please post your comment over here.