Why no flavor_USES helper?

[Mel Pilgrim]

The flavors helpers like flavor_RUN_DEPENDS are super useful, but I need 
to modify USES based on flavor, and find that there is no helper for it. 
 That is, I'd like to be able to do this:

flavor1_USES=   alice
flavor2_USES=   bob
Instead of:

.if ${FLAVOR} == flavor1
USES+=  alice
.elif ${FLAVOR} == flavor2
USES+=  bob
.endif

At a glance, it looks like all that's needed is adding USES to 
_FLAVOR_HELPERS_APPEND[1]. What am I missing?

1: Mk/bsd.port.mk, line 1525 as of bed4073e0