I never experienced it myself but it looks like the pre-clearance was planned to be available for BizAv as well since September last year.
Check here:
SHANNON - THE 51ST STATE - Aviation Articles - AvBuyer.com
Full contacts, including e-mails:
Shannon Airport - US CBP Facility
U.S. Customs & Border Protection
c/o Aer-Rianta
Shannon Airport
Shannon, County Clare, Ireland
Port Director
Phone: 011-353-6147-2297
U.S. Customs & Border Protection
Dublin International Airport
Pier B
Dubland, Ireland
Port Director
Phone: 011-353-1814-4818