This is a bit more complicated than dip and rinse, but if you have a lot to strip, maybe you can make it work.
Nickel is mined, going from the oxide to the metal, by reacting the ore with water gas, a mixture of H2 and CO (made by adding H2O to hot and/or burning coal - at the relatively low temperature of 50ºC and atmospheric pressure). Now the OP already has metallic nickel, so this step is redundant. The next step, formation of Ni(CO)4 obviously takes place at temperatures below 230ºC, because it decomposes there to nickel metal. Ref 1
The proposed operation is similar to mining, except that the nickel is discarded and the depleted ore (the brass item) is retained. First step, get some coal; start it burning (with a propane torch). Shut off its air supply and feed steam or water mist onto the coal (which will cool it, but also generate H2O and CO) and pass the water gas over the nickel-coated item. The burning coal will cool, so you have to run some air over it to heat it up again; then more water mist or steam to get more water gas to pass over the nickel-coated item. Repeat until all the nickel is gone from the item and deposited somewhere else, far, far away, because the Ni(CO)4 is terribly toxic and you don't want to have any contact with it - at all.
As I ponder the set-up, this method should work, but it does seem more like a theoretical exercise or possibly an industrial project, rather than a do-it-yourself type of chemistry. It could be improved, or simplified, perhaps, by getting a cylinder of carbon monoxide and passing it slowly over the nickel-coated brass item at a temperature high enough to form Ni(CO)4, but not decompose it, then lead the gas (excess CO plus the Ni(CO)4) thru a very long pipe to a hot zone where the Ni(CO)4 would be decomposed to metallic nickel and the relatively less toxic carbon monoxide.
If you try this, do appreciate the toxicity of nickel tetra carbonyl (Ref 2) and CO (Ref 3).
Ref 1. http://wwwchem.uwimona.edu.jm/courses/nickel.html
Ref 2. https://en.wikipedia.org/wiki/Nickel_tetracarbonyl
Ref 3. https://en.wikipedia.org/wiki/Carbon_monoxide