Well, it occurred to me that I could use probability to calculate the odds of finding a secret door when everyone is searching. Then, I could just make one d% roll and tell them if they've found something.
One of my players is a math genius and he reminded me that when you calculate probability, it is often easier to calculate the probability of something NOT happening -- in other words, 5 in 6 times a given (human) character won't find a secret door... If there's a whole bunch of folks searching; you multiply that 5/6 by 5/6 by 5/6... You get the idea; then you subtract that % from 1 to get the odds of FINDING a secret door. Easy peasy. :)
Taking that into consideration, I whipped up the following Google Doc
Here's what it looks like for my group:
Cack and Vera are both elves, so there's a "2" in the "finding" column. Oryx is a dwarf -- maybe he needs a "2" as well. Sir Owyn has "an eye for irregularity" so although he's human, he gets a "2" as well. Everyone else gets a "1".
When everyone searches, 92% of the time, they will find a secret door. If a few humans don't search, you just knock a few of the rows off the bottom. Of course, I can customize this at any time.
Hope you find that helpful!