I don't know if this is so much a short cut, as it is a way to not slow Poser to a crawl, but you could use a "cardboard cutout" method. Basically a flat plane with a texture of a person combined with a transparency map (to get rid of the excess surface area). Place a bunch of em around and it'd look like a crowd or audience. You could probably save the prop to your library and keep adding them in to your heart's content. Maybe make a couple of variant textures so not everybody is wearing the same outfit. Haven't actually tried this, but it sounds like it could work....