Joshua, if I may ask: would you mind elaborating a bit? Is it the fear of letting someone down, concern you may be making a mistake in passing, something else? All of the above? Thank you.
It's just hard to reject people. I'm an engineer type. I like looking at problems and solving them; the harder the better. The difficulty is often that the entrepreneur is the problem. Giving a real reason is tough.
Alternatively you could have an "I'll approach you" policy. Entrepreneurs would probably like that anyhow. You could say, "this is not a No, but I'll put you on my list to examine in the future, and will contact you if interested." Then have a private url form to which you could refer people to submit information. All of sudden, you're like YC.
You could give investor friends access to this form too, if the submitter wants to opt in.