A setting in the BO mapper?
No. Unless you create a custom property to return the value you want. It depends on where and when you are displaying a date value. You can just use teh native .NET formatting to specify what to show. For example, if you have a date field and want to show only the short date format....and not rely on the Short Date settings on the OS (a good idea for consistency at times) you can just use the MM/dd/yyyy.
MsgBox(String.Format({0:MM/dd/yyyy},DateTime.Now))
Anywhere that you use the formatting in SF this way (i.e. Lists, ListView, and Combos) you can supply the formatting like above.
For example, a column ina ListView:
{0:MM/dd/yyyy}