It is my belief, after speaking with the TTB, that you just need a separate entrance to the outside. The entrance to the distillery "warehouse" (bonded) can not be the same entrance that they use to enter the retail/tasting (unbonded/general) area. In effect, it makes it its own separate space. Here is an exceprt from the TTB agent -
"...completely separate the two areas and hence take that section off distillery premise. You could also use a solid wall with a glass window, but again it has to be floor to ceiling. The reason for this is that the regulations don’t really allow for a tasting room or retail on premise, so in order to make that happen, you need to make the division complete. Also, you need to make sure that the tasting room would have direct outside access..."