Exclude 1st Class Shipping method from certain products

I have a client who wants exclude “First-Class Mail? Parcel” USPS shipping method from two categories of her products. I found an extension “WooCommerce Conditional Shipping and Payments” that appears to do the trick, but this extension does so much more than she needs. Seems like a short code snippet should do the job but I can’t find one or anything close I can modify. Doesn’t anyone have a suggestion or place I can look. Thanks in advance.