I'm sorry that your question wasn't answered in a timely manner. To answer you directly, no, there's too much skin involved (miliary dermatitis due to a flea saliva allergy) to treat topically (other than with a flea product). Cats will lick and ingest products placed on the skin often to their detriment.
Miliary dermatitis is a papulocrustous (crusty bumps) eruption seen mainly secondary to allergic skin disease. In rarer cases we'll find the demodectic mange mite which can be found upon examining skin scrapings microscopically.
Whenever the area between the edge of a cat's rib cage to the tail is involved, a flea saliva allergy is most likely. Even if you can't find any fleas, it's best that you apply an effective over the counter flea spot-on such as Advantage/Advocate or a fipronil-containing product such as Frontline or one of the newer flea spot-ons available from Charlie's vet because many flea populations are now resistant to the fipronil in Frontline. In severe cases we can either inject or orally administer a prescription antihistaminic glucocorticoid (steroid) such as prednisolone which often works wonders in these cats. Antihistamines such as diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton) aren't reliably effective against allergic skin disease but you might see how a dose of 2mg of an over the counter chlorpheniramine once or twice daily affects Charlie. Please note that cats can be such effective groomers as to remove all evidence of fleas. It's important to still use the flea products.
Less commonly but still important, Charlie's skin can result from a food intolerance or atopy (allergies to environmental allergens such as pollens, molds, dust and dust mites, etc.) Food intolerance/allergy is addressed with prescription hypoallergenic diets. These special foods contain just one novel (rabbit, duck, e.g.) animal protein or proteins that have been chemically altered (hydrolyzed) to the point that hisimmune system doesn't "see" anything to be allergic to. The over the counter hypoallergenic foods too often contain proteins not listed on the label - soy is a common one - and these proteins would confound our evaluation of the efficacy of the hypoallergenic diet. The prescription foods are available from his vet. There are many novel protein foods and a prototypical hydrolyzed protein food is Hill’s Prescription Diet z/d ultra (my preference). A positive response is usually seen within a few weeks if we’ve eliminated the offending food allergen.
Atopy is usually initially addressed by the same prednisolone I mentioned above and used to address a flea saliva allergy. Prednisolone can be used as a test when differentiating a flea saliva allergy or atopy from a food intolerance. Both a flea saliva allergy and atopy are usually quite responsive to prednisolone. Not so a food intolerance. Please respond with further questions or concerns if you wish.