Everyone forges their own recommendations. OK, not everyone, but most people write their own or provide a heck of a lot of "guidance" during the process. I know this because I'm on the "sell side" of the admissions transaction. (Wow, I sound like an investment banker.) My students constantly ask what they should write in their recommendations.
It isn't that applicants are trying to cheat the system; the problem is that most recommenders don't want to take the time to respond to the online questions and fill in the "grid boxes" that are part of most MBA recommendations. So they ask the applicant to do the dirty work and agree to endorse the finished product.
You'd almost be crazy to let your boss write your recs. Frankly, he has no idea what he's doing and he can inadvertently screw up your chances of being admitted. I see it all the time. To avoid that problem, I recommend that my students give their recommenders a list of the questions they'll be asked to respond to and to provide them with some appropriate responses. (We give these to the applicants we work with.)
Don't leave your fate in your boss's hands. He's a clown who doesn't know what he's doing. Give him some guidelines, and if he asks you to complete the recommendation forms yourself, don't hesitate to do so. The schools all know that many of the recommendations are from the applicants themselves. (Yes, I've confirmed it with the admissions people.)
This is a tough situation. Schools hear this question from hundreds of applicants every year. They always answer something like, "Well, just do the best you can," which is a lame response.
My suggestion is that you get a recommendation from a coworker, a former employer or one of your customers. Most schools want two recommendations, but if you can't get them from your boss, get them from whoever is available. That causes a lot of worry, but in the end it rarely makes any difference. The schools will understand.
You may hear from some admissions people that they put a great deal of emphasis on letters of recommendation. I hope, for the sake of applicants, that they're bluffing to justify putting your recommenders through an arduous process. The quality of your recommendation is so closely tied to your recommender's ability to write that it wouldn't be fair to place much emphasis on it. Some recommenders are very good writers, and some have even gone to top MBA schools and know what to write about. Others are terrible writers and don't know what the admissions people are looking for. That's why the recommendations shouldn't be taken too seriously.
If you don't believe that the recommendation is more reflective of the writer than of the applicant, then have your boss write a letter for you. I'll make up a recommendation for your officemate (against whom you're competing for a spot at Wharton). You can judge for yourself which candidate looks better on paper.