Let us examine the ways ♭$\hat{6}$ can be harmonized as root, 3rd, 5th, and 7th of a borrowed chord.
Here are the ways ♭$\hat{3}$ and ♭$\hat{7}$ can each be harmonized as root, 3rd, and 5th of a borrowed chord (notice some of these chords are duplicates from the previous example).