My understanding is that it really not recommended. Since Cub Scouting is a family program, the ideal is to get more parents involved, although I know this can be difficult. There might be situations which are the exception, but in general it would be better to find another parent to serve as den leader for the second den. Then you could be a den leader for one den and an assistant den leader for another den. Providing a quality program for one den requires a lot of time. If you are trying to do this for two dens, it can be even more challenging.
Readers, what do you think? Add your ideas to the comments below.