There's various ways to treat it and it depends whether it is true sciatic pain or referred pain. As well as this, it depends on which movements cause the pain, typically it's prolonged sitting or bending forward. In the short term, heat will provide some relief as well as limiting the time in sitting or in the aggravating position. NSAIDs and analgesics such as Voltaren or Advil may also help however depending on the nature of the irritation results will vary. I would recommend seeing a physiotherapist. It is hard to choose treatment without seeing the movement patterns or having a history.
If it is related to a "slipped disc"....
Basically discs don't slip. It takes a lot for something to move in the spine it is a strong structural base of support so the term slipped can be discerning. Most likely, the pain that they are getting down the leg is referred pain. The discs are like fluid filled sacks, they are designed to allow movement between each vertebra in each range of motion. If you spend too much time in flex ion (sitting) with poor posture and poor core activation. The fluid gradually protrudes a little towards the posterior aspect and can push onto the nerve endings that come out the back. The nerve roots become aggravated and cause the pain down the leg in the region that that nerve root is related to.
I would say limit the amount of sitting, review their desk or car set up, and possibly get a rolled up towel and sit it in the arch of their lower back in chairs with poor support.
Then a Physio can provide manual therapy to try and normalise the position of the disc, as well as core activation exercises to prevent long term.
Sports Medicine Trainer at Sydney Grammar School and Physiotherapist at Wolper Jewish Hospital