I called PTC about this last year and there is no way to do it other
than replacing the default balloon. From the ticket:
As per current Pro/ENGINEER functionality, it is not possible to set a
custom BOM balloon as reference balloon with in Pro/ENGINEER UI.
However, user may accomplish this using the procedure given below.
Within Pro/ENGINEER <loadpint>\symbols\report\bomballoon folder, there
are two default reference balloon symbols. 1) smp_ref_bln.sym (without
Quantity) & 2) qty_ref_bln.sym (with Quantity).
If user intends to use custom reference balloons, these files should be
replaced with user's custom balloon symbols. User should make sure that
the custom balloon placed for "smp_ref_bln.sym" should not have any
quantity text defined in it and the 'qty_ref_bln.sym' should have
quantity text defined.
Christopher Rees - Mechanical Engineer - ISR Systems
UTC AEROSPACE SYSTEMS
100 Wooster Heights Rd, Danbury, CT 06770 U.S.A.