The article is very good and makes it clear that a trust established during the lifetime of the decedent could be the beneficiary of the IRA. I have seen people establish such a trust and fund it with $1. However, as you note, in this instance the testamentary trust and the passage of the IRA funds by operation of law would both take effect at the moment of death. I'm just not certain it will work, but your bank must be certain when it comes time to make the payment.
Talk to your bank's attorney and see if he thinks you should require an indemnification and hold harmless agreement with the customer regarding the beneficiary designation. Know that the other attorney will be indignant at any suggestion that the plan is not perfect, so your attorney may need to do a little research before you bring it up. It's an issue of state law, not the Internal Revenue Code.
"Never take advice from the other guy's lawyer." Me