So far as the smoke scenario is concerned, the bag is pretty useless and counterproductive. However, you can rip the bag off the hose, stick the hose up your nose and then cover your face with (preferably wet) clothing as a filter. For hoses which have an inline expiration check valve, the other option is to disconnect the hose from the valve (usually just a simple hose over spigot fit) and use the supply hose end up your nose .. this one depends how long the hose from the supply to the valve is.
An interesting challenge for the seatback safety card cartoonists.
Outside the technical discussions, though, I'd be worried at doing anything to the cabin at a time like that, that the cabin crew wasn't prepared for. If it's not in company procedures for the flight deck, it won't be anywhere else. Dropping the masks would signal decompression to the cabin crew, and increase their workload at a bad time.
The passenger oxygen system isn't designed for this, it hasn't been tested for this, it's there for a completely different reason. Is that something to add to the mix at a time when there are probably enough unknowns to be getting on with?
R