Cubdriver

I assume you have single engine commercial with instrument privileges. What you want to do is take the 4 day ATP multiengine/instrument/commercial add-on course and bump it all up to multiengine in one glorious SHAZAMMM [strobe light burst, gaffer changes props, makeup rushes in and out]... You are a now a multiengine/instrument/commercial pilot, and all in only 4 days of trudging the halls at ATP interspersed with short frantic flights in a Seminole, popcorn breaks where you fight with the FBO girl over where you can and cannot put your flight bag, plus watch really rich people pile out of learjets with countless pets pile into a black mercedes.

I am no genius...ok yeah well allright I sort of am and some say a legend in my own time but... I am aware of one real advantage to doing it step by step going through single engine aircraft to get your commercial and instrument ticket rather than doing them all initially in a multiengine: rather than getting your commercial and instrument in a multiengine airplane initially skipping single, if you go through single (Cessna 172RG, Cessna 182RG, M20 and the like) and wait until the end to go for your multi you avoid having to go back and add single engine commercial and instrument afterwards. Seriously.

I have a friend who got his commercial and instrument in a Seminole all at once, and he has only a private pilot rating in singles to this day. When he flies a C172 he is only a private pilot, and how insulting that must be. I don't think he aspires to doing traffic watch or pipeline patrol any time soon, or shooting approaches alone in a Cessna 172 when he owns a Cessna 310, but it is a silly rule worth mentioning so as to avoid. Do your commercial and instrument in a single before getting your multi is the point.