Some of the ink configurations of these devices allow the use of White, Varnish, and/or Primer as Spot Inks. To configure them, you need to:
1- Use the proper driver for your printer. In this example, the CMYKGLW driver allows the use of White and Gloss.
2- Select the right resolution and quality to achieve the wanted effect (For example White->CMYKOrRe, to have White under colors in one shot).
3- Then go to the Page Setup module:
4- Open the corresponding tab, and then click on Enable separation:
Info
To have more details on the topic, please refer to this article dedicated to Spot Inks.