Hey. Is there any way to make odoo work with negative values for time offs?

Our company sometimes round a number of time off days employee get. For example if employee has 6.1 days on balance we may give him 7 days off.

Sometimes we may add extra days for vacation over yearly cap of vacation days. 

So the question is, how can we implement it with odoo? Basically i want odoo to allow me to give more time off days than what employee currently has, and display it in employee page with negative values.