The post you reference is wrong on several counts.
First, the TN prohibition on self-employment relates to who writes the letter for the TN. A self-employed individual seeking TC status under the old Canada-US Free Trade agreement could write his or her own TC letter, since he or she was the employer. This loophole has now been closed. What it means is that a self-employed person can still seek TN status, but the end client needs to write the TN letter or file the I-129.
Second, there is NO prohibition on being paid via 1099 on a TN. The poster is confusing this with the H-1, which does require a W-2 employee relationship.