Someone asked a great question here - "What would you do if not so many people showed up for a World Cafe - or they were tired?"
People who do David Bohm-style Dialogue have had very successful experiences with less than ten people. Dialogue group can accommodate up to thirty people, but any more than that gets too big and there ends up being a competition for talking time. So this is one reason why the World Cafe format works better for larger groups. Also people are not intimidated by the public speaking skill challenge that is stimulated by being in a larger group.
Any two people can have a Bohmian-style conversation, because the ability to Dialogue is an attitude about freedom, suspension of the reaction to need to come to a conclusion, acknowledgment of believability and curiosity. Of course, this is much the same features that a great World Cafe would have!
The objective that World Cafe and Bohmian Dialog have in common is to "think together, to go places no member has ever been before by themselves or in the past." Of course, using a argument-based debate style is not particularly constructive for the goal of this experiment.
If you wanted to do a David Bohm-style Dialogue in this situation, the main feature that you would explain to people is freedom. Specifically, freedom to allow the subject of what you're talking about to go anywhere it wants to go. Generally, this means that the subject matter is improvised on the spot - people are not obligated to keep to the subject at hand.
There are a few helpful skills in Dialogue. First, there is no need to "convince," because everyone already has been granted the status of being believed as their own authority.
The second useful skill is the ability to suspend coming to a conclusion or to put off judging outcome.
Third but not required: It is always handy to have someone who is able to generalize. Describing relationships of what subjects emerge as the conversation progresses is handy to hear - as a reviewer does - but without applying taste or judgment to results. This helps to compensate for the "point to point" tendency of jumping from one idiosyncratic association to another that people tend to have and allows for harvesting.
To start a David Bohm-style Dialogue, people would toss out multiple questions or comments about any subject. Perhaps if they have come together already expecting to talk about a particular subject this would be fine to use for a start. Others comment on whatever subject(s) that have been introduced that they would like to continue investigating, or they start their own, possibly unrelated subject. While this is happening, the subject everyone seems to want to talk about "takes off" and it becomes obvious that the conversation is in process.
Anyway - that's enough of an outline for anyone to use Dialogue on the fly next time you might run into that situation of not enough people for a World Cafe. Let me know if you'd like to hear more about Bohmian-style dialogue with specific questions...