While many schools offer a MEL CPL, some also offer to do a SE addon after the commercial checkride. While at this time you do not foresee using your single engine rating commercially, times change and opportunities are what they are. I have seen guys miss out on excellent opportunities because they didn't have the proper commercial ratings.
Whatever school you are going to check with them about the possibility of doing the SE add-on and cost. Depending on the examiner, what you have to do should be limited to normal SE maneuvers and the maneuvers that are not done in the ME.
Good luck.