The ovens do go above 350,
I assumed that. I was talking about their possible concern about the oven temperature, because I thought perhaps they worked out what temperature the food will end up at if the oven is set at 350°F. I've seen pizza recipes floating around that bake at 350°F, but comments to the effect of needing to raise the temperature are usually put forth in response to trying those recipes. I think you're just going to have to use a standard whole grain formula baked at the lower temperature and see if they like it. I doubt you'll find one explicitly given as a low temperature formula. You should also remind them, if you haven't already, that Mexican restaurants that try to serve Chinese food don't do well. In other words, cook food that's appropriate for the parameters of your business. Pizza is a high heat food product.
