Anyway, I just want to go into the Campaign and send it to one person.

You already have a feature very close to this - when sending a Test. While developing a campaign, I can send tests to anyone. Why can't we have this AFTER  the campaign has been sent?

I know, there's a caveat, and that's in the use of merge tags. Most of the time I only use FNAME, but maybe you could check if the email is in the mailing list and pull the details from their record as usual?