just from a google search, I found mention that the blow bypass valve was vacuum operated.
with high manifold vacuum (and boost not needed) the butterfly opens and reduces the parisitic load of an useless blower.
with loss of manifold vacuum (accelerating or high power demand) the butterfly closes.
maybe just disconnecting the vacuum hose would do the same as the tie wrapes, but it sounds like a feature you would want
please note this is just keyboard mechanic/engineering as I an humbled by your work