The lesions you are describing are consistent with lesions known as lick grnaulomas, a condition which most commonly occurs from excessive licking of the paws due to allergy. The most common type of growth on the paw pads of dogs are actually lick granulomas. These types of lesions are started typically because of allergy, likely to grass, weeds, pollen, or other allergens that collect in the grass and come in contact with the feet. Usually the dog licks, which leads to more inflammation, hair follicles get clogged and infected, and then the lesion begins to build on itself getting gradually ever larger. The technical scientific term for this condition is actually furunculosis.
This can be one of the most frustrating skin lesions we see in veterinary medicine, since both getting the dog to stop licking and controlling the allergy are very difficult. Also, as the lesion gets larger, it becomes increasingly difficult to manage medically, with many quickly degrading into a surgical case. Therefore, it is necessary to treat both aggressively and as long as necessary (often 6-8 weeks) to get this under control right off the get go.
I would approach this initially first and foremost by making certain that the dog is not licking the area, by putting an elizabethan collar on him for the next several days to weeks. If you do not keep the dog's mouth off the mass, no treatments will ever be successful. I would leave this on for as long as necessary to clear the mass.
Next, I would address the potential allergic component as the inciting cause, and treat with the over the counter antihistamine, Benadryl. Benadryl is both safe and effective for managing skin allergies in dogs. It is dosed at 1 mg per pound of body weight, administered orally, three times daily. I would treat for 6-8 weeks.
You should also purchase over the counter Epsom Salts to soak the affected paw in a warm solution for 15 minutes 3 times weekly for 6-8 weeks.
Finally, you should thoroughly wipe and clean the mass once daily with a benzoyl peroxide based skin cleanser. Stridex Pads are a good example of this, as well as a similar product made by neutrogena. The key is the main ingredient being benzoyl peroxide. On days that the foot is to be soaked in Epsom Salts, wipe the area with benzoyl peroxide pads after the soaking when the paw is dry.
All of these treatments are designed to reduce inflammation, suppress the allergy, and de-clog the hair follicles. Ideally I would want to do this with a concurrent long term course of antibiotics to also reduce infection, but if the lesion is not very large at this point, you may be able to get away without it, and at any rate, it would require a visit with a veterinarian to acquire antibiotics anyway.
If within a couple of weeks, these measures do not begin to offer significant improvement, then the mass could be some other type of lesion, perhaps even a tumor. Skin tumors can arise from the foot pads and from between the toes, ranging from benign masses (not cancerous) to aggressively malignant (cancerous) masses. Therefore, if things worsen or do not begin to improve after a week or two of treatment, then I would make certain to get the dog to a vet ASAP.