Change Display Decimals on Unit Cost

Has anyone changed the number of display decimals on the unit cost field (UNCS)? 

We have items that are inventoried in impressions (IM), and each impression costs less than a penny, so we cannot specify a cost with much precision.  Since we have 0 decimals in our quantity fields, we cannot change our primary UOM to thousand impressions.  Changing the primary UOM to FT or LB would also not help because the cost is also very small per foot or pound.

Changing the display decimals on the quantity fields would be a huge challenge.  Instead, we would like to change the display decimals on the unit cost from 4 to 7.