When you have a true OFAC hit and the funds must be blocked (frozen), you place them in a separate interest-bearing account. [It must bear interest at a "commercially reasonable rate." That means a rate currently offered to other depositors on deposits or instruments of comparable size and maturity.] The title to the account is still held in the name of the designated individual, entity or organization, but that individual or entity cannot exercise the pwoers and privileges normally associated with ownership unless authorization is obtained from OFAC.
You would use the owner's identifying number as the TIN on the account.