Hi, Steve. There are 2 alternatives that are safe and still give you a good, long lasting finish. For regular, constant food prep use, of course, mineral oil is the standard, but I can see why you do not want to apply it every couple of months. But with any butcher block, it would seem that the possibility would occur for someone using it that way. If you go with either of these 2 choices, you will be safe now and in the future.
The first is Behlen Salad Bowl Finish which is available from Woodcraft stores and mail order. They have a web site (www.woodcraft.com). The second is shellac, which is available at any home center or paint store and many mass merchandisers. Be sure to check the date on the can and reject any that is more than 5 months old. Find another store if the first place you find it only has old stock. The shellac is not advertised as being food safe, but since shellac is used for pill coatings in the pharmacutical industry, it is still a pretty safe choice. And, again, both will give you great finishes.
Since the thinner for the Salad Bowl Finish is paint thinner/mineral spirits and the thinner for shellac is alcohol, be sure that you apply them away from any flames or sources of ignition and where there is good ventilation. And be careful with any rags used. Leave them outside for a day or two so all the solvent evaporates before you bring them in to pitch. Follow the manufacturers instructions and warnings on the cans.