This is really a genuine disease that comes from within the genetic code of the dog. Have they worked with their vet at all on their end for the overall health of the dog? Do they have a care program they do at home at all?
It isn't possible to get it to end from where we stand in the salon each day. But- we can help.
You mentioned that you are using oils to help soften the growths and that does help. Keeping the pads well hydrated does help them to shed better and lessen the hardness of the feet for walking. The same goes for their noses- while most anything we apply to the nose will be licked off superficially, rubbing it well into the skin will give added benefit if you take the time to apply it well. For the nose it is very important to not use anything with strong scent as this can be irritating to the pet. I have Dr. Rose Remedies salve and I like it for things like this. On the paw pads, what I do for those who have overgrown callous, dry cracked feet or weepy nail beds from yeast is first a vinegar soak. Plain apple cider vinegar for 3 to 5 minutes before their bath. Then I wet the dog down to get ready to apply their shampoo. Then I go back & pack the feet & cover the pads with colloidal oatmeal powder that I wet with my fingers so it is like a paste. I leave that on while I wash the entire dog. I wash the feet last with the same shampoo I used on the pet. Then I rinse it out completely as I rinse the rest of the dog before the end of the bath. I will try to rub off as much off the dead callous as possible while rinsing the pet and that leaves the pad more open to absorb topical moisture products. On my table, I apply the Paw Massage Oil that I have which is available from my Canine Spa Therapies product line- its base is Extra Virgin Olive & Vitamin E oils, but you could possibly make your own to have on hand with simple knowledge of oils and how certain ones benefit the body. (However, it is readily available for the pet industry!) I rub this in very thoroughly before I even blow dry the dog so that it can absorb for the rest of their visit. Both of these oils are fast absorbers and help repair and encourage emerging new skin cell layers. From there, I finish the groom, and let that sink into the feet well. After the groom, I lift each foot and apply either my Paw Balm from Canine Spa Therapies, or I also like Davis' Pad Repair Cream as well. Rub this in well so that you know it won't get all over the client or their car. In one case, I do have a dog that comes in just for feet care between grooms. The dog gets the feet washed, packed, exfoliated, then I apply warmed oil and leave that on under the rubber slip on booties (they look like a deflated balloon) for about 10 minutes. They then come off & the pet gets the Paw Balm, the nail trim, and a paw massage during the course of this care. I have also heard of other groomers applying pure Vit.E oil with a cotton ball to the feet, or applying Bag Balm, or pure Bees Wax, or just even a heavy duty grooming industry paw cream or balm can help moisturize. I would not go with just a simple wax since you want attributes within the wax, cream or oils that genuinely penetrate and offer their healing properties for the damaged skin cells.
The problem with this disease is the way that it tells the body to keep creating keratin layers- so it is important to not do anything to the feet by deep mechanical exfoliation that will tell the skin to work on repairing damage- or we could make it worse. Just keeping the feet moist gives comfort and us removing what is very ready to come off will help with buildup that also causes discomfort.
Also, I ask that these clients have their pets in for regular nail trims so that I am sure the feet get pressure on them evenly and not have any additional pain from overgrown nails.
Human kindness has never weakened the stamina or softened the fiber of a free people. A nation does not have to be cruel to be tough. ~Franklin D. Roosevelt