mentions that by mixing the input with 2 x the BP filter, you'll get an all pass filter. The same does this pdf:
I tried this with some success. I had to disconnect the 33k resonance resistor, but after this I got a response with a slight 667 mdB notch.
I will try breadboarding this later.
The MT-223-pdf also mentions an alternative way of doing a notch filter:
Which gives this notch:
As opposed to the notch we get by mixing LP and HP: