Has anyone ever looked into plumbing their dust dropout bin (the bottom of their air filter) back into their Separator Inlet? This would use an inline blast gate that is normally closed to stop airflow when the DC is in use. Then, periodically just opening the blast gate for a second or two to purge the dust that has fallen out of the filter and sucking it back into the separator for another chance to be separated? This could eliminate the need to empty out the dust bin.
I can't say how well it works, but here is the same concept with a cyclone...
http://www.pennstateind.com/store/TEMP2PCX.html
Mark