I had the same problem like you and because I didn't find some solution I decided to make it.
After 3 days of testing, sending PHP to hell and back I can say now I have done it, yeeeeeeaaaaa.
Solution of this is not so easy. It is neccessary to modify PHP code in 3 files, also modify DTB SQL table (add one field) and if you want then modify lang PHP to add new options (or you can write it strict to code in your language).
I tested it and it really works. I think it would be integrated to new version maybe because it is quiete helpful feature, isn't it? But it is question for Ted, not for me.
Anyway, it is not so easy and I will prepare detailed description how to do it and how make any of block non-searchable or searchable (after this modification you will have choice of it, when you make new or edit old block). I will try to write description step by step today but I'm very bussy so give me 2 days please
