The easy or hard gold dropping in the Cops And Roppers gameplay mode depends by the bound of the used car; with many add-on ones results harder do that, and isn't possible edit this most of the times.
Here's the CNR Gold Drop Mod that makes the gold easy to drop for the game default Audi TT and Panoz GTR-1 cars. To download it is needed a registration to the MM2BR website, and use Firefox browser to get the .zip file without problems.