on #1 at least the catalogs i've seen have pretty poorly defined boundaries for DSOs - sometimes just a circle.
#2 would be really interesting to have, though juan has been working on a new background extraction tool. maybe the sampling will not be necessary, who knows.
what i usually do is cheat - find a good image online ostensibly taken from a dark site, then register it to my master and place the samples on the registered good image... then save the process icon for DBE and quit DBE. then i run the process icon against my image, tweak the tolerance, and execute.
rob