I'll bet you can get around the rule. Go sit down with the director of the daycare and have a little chat. If the issue is that they lack the refrigeration to keep the food cold, then tell them you'll bring the food in a little insulated cooler with a coldpack inside. If the issue is licensing or state regulations, have them show you the exact wording of the regulation, and then tell them that you'll bring a physician's note that they can keep on file for the regulators. (Your pediatrician will be happy to write such a note stating that the baby must have homemade baby food.) If they are worried that you'll have remember to bring food in everyday, instead of just stockpiling a month's supply, then reassure them on that point. Most likely no one has ever asked to do this, so they haven't had to think of their solution. If they bring up an objection, just smile sweetly and ask if the two of you can brainstorm together to think of a solution, and then offer a possible idea.
I never had problem bringing in homemade food, but I was told that cloth diapers were against state regulations. I read the regulation carefully, and figured out that if I got a doctor's note, the regulation would still be satisfied, and the owner agreed to let us use cloth diapers. My dd was and is the only child in the history of that daycare to use cloth diapers, so it was just that they had never given the issue much thought and that their knee jerk reaction was to forbid it. But they were perfectly willing to try unorthodox solutions, as long as their license would not be in jeopardy.