dzug, I think this is one of the most complicated questions ever on here, albeit a relatively simple answer!!
Assuming the bequest is to set up the Joe Bloggs Charitable Foundation for Distressed and Disturbed ABers. Assuming that this is a charitable object (some things may appear charitable but are not), the CTO should accept the fact that the bequest is charitable (claim charity exemption on the IHT form) and then the Trustees register the charity with the CC. No IHT is paid.
The same result would occur if you leave your estate to "charity at the discretion of my executor". That will be IHT free.
However, setting up a charitable fund by will is a right pain in the neck. I would always advise that the testator try and choose a pre existing charity who is an incorporate body, but with a "cy pres" clause just in case that folds. That will ensure that the money goes to charity in perpetuity.