Randomizing PO number generation

PO numbers are generated sequentially by default, which gives our more savvy vendors some insight as to the volume of orders we are placing with other vendors.  We would like to limit this visibility so that suppliers are unable to determine the number of orders being placed between two discrete orders placed with the same supplier.  Rather than creating PO numbers in sequential order, is it possible to generate the PO numbers in a quasi-random fashion, such that the new PO numbers are always unique? 

Or, has anyone come up with an alternative solution to a similar problem?  Thanks for any feedback!