Suggesting reviewers for a very sectorial double-blind submission The topic of suggesting reviewers to a journal has been covered here multiple times, for example on how to pick them or whether it is (always) good practice to actually follow the suggestion.

I have a different doubt that I do not find covered in other questions, that arise from the following conditions: 


As I think very highly of my paper (who doesn't of their own!) I want to suggest very reputable and expert reviewers; I need 5 at least; 
The topic of the paper is very sectorial, and adds to a very small community;
The paper has been previously presented at a conference with no proceedings;
The journal follows the double-blind review process.


As a result of this, I am at short of qualified reviewers to pick: most of the people I could indicate (which are several) already know about the paper (as they were at the conference, or I know for a fact that they already read it); these are not colleagues, and a review from them would not imply any "conflict of interest", but will certainly break blidness as they would know right away who wrote the paper.

It seems rather silly to include their names in the list of reviewers knowing that, was the editor to invite them, they would have to refuse to review it.

On the other hand, the list of highly qualified people that would make for an excellent reviewer is too short without any of those names included!

Should I:


Include them anyway and specify that they may know about the paper because of its presentation at conference X?
Suggest less qualified reviewers, accepting the risk that a) the suggest reviewer may dislike the paper or b) the reviewer may not necessarily "impress" the editor?
Submit the paper with less than the required number of reviewers, if the system allows me to?
I would suggest (1), with a tweak. There is no need to mention that these reviewers may have seen it at a conference. As you said, it does not constitute a conflict of interest. That is the only reason you should mention additional information about a reviewer.

Let's be clear, there is nothing illegal about a reviewer having come across your work earlier. It may break blindness, but then, blindness is often broken in double blind reviews for various reasons (small communities, typical writing style, figure formats etc.). This does not really compromise the review. The only exception I see is if the reviewer is a petty competitor, who would use his prior knowledge to rule against your paper.

If you feel that any of these reviewers may be biased against the work, don't suggest them as preferred reviewers, regardless of their standing.