Take a look at this:
Abusive Tax Shelters
It is pretty dry reading, but it seems that these things have two pretty big weaknesses: The use of "trust protectors" who leave data and paper trails between the trustees and the grantors/beneficiaries (thus expsing the trust to be false on its face) , and the possiblity that one of the trustees might get ideas and ignore the "trust protectors" and do things his/her/its way. (as what hapenned with Proteus AG).
Now imagine a Sixth World slant. Imagine that comunication between Grantor and Trustees is done in special drops in code in the Astral, or that the Trust Protectors are spirits (say, Task, Guidance, or Man) bound to the Grantor, able to relay their master's wishes the moment he makes the descision, and with enough Force and Power to punish an unruly trustee. How about the trustee being a Free Spirit being blackmailed by a Grantor with knowlege of it's True Name to keep it in check?
Maybe it's the work of a coterie of Shedim with a Master Shedit devising the financial instruments and running the show. He could even be offering services to mundane clients in return for, ahem, quid pro quo.
Anyone else want to chime in?