Rik:
I like Joe Wein's suggestion.
There are a lot of things that go into this kind of checking... (factoring domain registration dates, factoring in a domain's nameserver, etc.) ...plus other checks to make sure that legitimate mail doesn't get into the spamtrap. On top of all of this, you also have to watch out for innocent parties being backlisted due to a spammer's "Joe Jobs" attack (where the spammer tries to make it look like the spam came from another innocent party). Finally, Rik, even if you have to skills to do all this, Joe Wein may be able to do it faster and with less meticulous hand testing due to the extensive tools and knowledge he has developed. It if obvious from his web site that he had successfully dealt with all of these harder issues before.
I'd say that your spamtrap and Joe Wein's extraction/checking process would make a great combination. It would likely be a very wonderful contribution to SURBL if you took him up on this offer.
Rob McEwen