Matt Whiting wrote:

Is this an "official" FAA procedure or just something that most
controllers understand as an indication that FF will be requested?

I've never seen it published, but it is known to work. Oakland
actually encourages it for VFR class B transitions. It's how
ADIZ and FRZ flight plans get routed in the DC Area as well (although
you are not authorized to use that ploy to get ADIZ flight plans
for VFRs).