You can do your MEI as your initial if you like, that is what I did because I did it under the VA and got reimbursed for most of it.
As others have said, only useful if you plan on going right from MEI to double I and single I. A MEI in itself is almost next to useless and you would be hard pressed to find a school to hire you low time as an exclusive MEI guy.
It can definately be done though, but it is a lot of work. I had 130 hours ME when I finished it so I just felt more proficient in the twin than a single so it seemed like the logical plane to do the most difficult ride in. On the other hand if you have 15 ME from your commercial then I wouldnt reccomend it, the ride is a little to complex to not feel 100 percent in the plane