Apply Conditional Formatting on Resource Usage view in MS Project?

Hi,
I'm using MS Project 2007 and noticed that you cannot see individual resources' vacations in the resource usage view (i.e. the cells are not greyed out in the same manner as weekends & global holidays).
As a workaround, I was wondering if it is possible to apply a conditional format to cells in the resource usage view in MS Project.

For example, if the remaining availability on a particular day is blank, then shade the cell in black.

Help?!