It isn't the most likely candidate to make someone a millionaire, but it's theoretically possible.With the company's market cap of $28 billion today, it's important to recognize that DexCom (DXCM -1.49%) is already one of the world's biggest medical device manufacturers. It therefore isn't likely to explode higher in value overnight, or even over the course of a couple of years.If it's going to be capable of making its investors into millionaires, those investors will need to commit a substantial amount of ...