You can all so script a prim to go beyond the viewers limits

default
{
state_entry()
{
llSetScale( <0.001, 1.0, 256.0> );
}
}

All so the hallow of a box or other shape may look like it has more then one side but the entire hallow is treated as one face.

I use this in SL all the time, you can do it with cylinders if there not hollowed, cut in half should be ok too, torus, and tubes can some times be included in a link set with other prims set to convex, and not have the count go up if their set to type none. I went to test it in Kitely after seeing ...