Polycom's response does not seem to address the first part of the original request:
" Is there a way to disable the Directed Call Pickup feature when using BLF? "
I have found that
<feature.directedCallPickup.enabled="0">
does not seem to have the desired effect in preventing the feature with the BLF, in my testing with a SPIP 670 on release 4.0. I am interested in the answer to this question. Thank you.