Using Field Security against Sales Order Entry/Salespersons?

Most of the time Field Security is simple and straight forward, however, it appears nto with Sales Order Entry and 'salespersons'.

I know that it's stored under orderhed.salesreplist in a single field as a horrible array/delimeted field (I'm presuming that this is still the same in Epicor 9 ?), but adding Field Security to this has no effect on whether or not a user can enter/view data on a Salesperson.

Is it possible to achieve this, or is the horrble way that this operates on Sales Order Entry effectively making this impossible ?.