Before the pandemic it was forbidden, and I believe that is still the case.
I've worked with capable pax to split up into small groups of 4-6 and have them enter through different doors and spaced in time to just "take a stroll" inside.
Coordinating bus drop and pickups (I dropped in front of Grace Cathedral) can be tricky and a bit of a crapshoot) based on activities in the area.
Not all groups are capable of executing, so careful thought must preceed the decision to go.
You could also drop on Powell if that entrance is open, (you must check) and then walk the hall and go up the elevator.