Skip the preview since you've already read it you have a general idea of what the book is about. Since you've most probably forgotton consciously most of the book anyway why should it have any impact. When direct learning you need not limit yourself just to five books you can include it with others you haven't read.
I think Pauls point about previewing too much just before doing the direct learning exercise... is becoming concerned if we can absorb it all. Worrying about what we think we need to know etc. Creating barriers to absorbing the information before you start.
Now if you are worried that including that book will have a negative impact on the direct learning process you may as well exclude it. The worry or concern you are creating will be exactly the problem you are looking for. A self fulfilling prophecy.
Personally I think if you keep an open mind about it just include it amongst the others you will still absorb the beneficial information form it.
Rather than worry about it, whether you're doing it right or including a book you've already read is going to work (if anything it might not work for that book but the others would still kick in). Play with it, take the attitude of lets see what will happen if? Don't worry if you don't get it perfectly right the first time. With the goals you have in mind I would hardly stop at 5 books, 5 books to a session yes but on the subject? Afterall if you didn't have the direct learning technique you'd have to do it the old fashioned way, which takes longer.
Worry if you do it right...you'll see the results of your worry.
Play, see what happens ... you learn what works and shrug off what doesn't but everything you discover that works for you becomes a gem that you own.
My suggestion, don't worry about it just try it and see. You are a unique being so only you can really tell what works for you.