I just did a test , placed 10 object randomly created a closed element then placed fence by element clip
then fence file out to new file and all the elements inside including the bounding polygon ended up in my new file
I ended up creating the scrip for this a few weeks ago as I was trying to approximate some gis work methods without gis not being at work I cant do the full script here
but it was something like this ( attache it to an F key}
place fence element;%d;fence file=
But I dont know how to control the type of fence ie clip or inside
I also found old post that has macro with a lot of what you want take a look
communities.bentley.com/.../192148.aspx
ok did a trial and error fut this in a F key
place fence element;lock fence clip;%d;ff=
works for me perfect even integrity of polygon is maintained... stays complex shape...