You have a few options.
1. Since it is a blue label you can crack it yourself and then you would have the peace of mind on how it will be handled when the case is opened (not saying CGC will mishandle just lowers the chances of any oops on their side). Of course by that token if you slip it is completely on you. If you do it this way, please keep the label so you can report it to CGC this is that label for census purposes.
2. Take it still slabbed to where Neal is signing, making sure there will be a CGC witness and have them facilitate the signing. They will crack the case, get it signed, and submit it to CGC. This is in the instance it is a "private" screening.
3. Take it still slabbed to a convention where Neal is attending. Go to a CGC booth (if they are also attending). Sign up for a witness to follow you to witness the signature. You at that point can either ask them to crack it or have it already cracked and prepared (bring the label with you if you already cracked for Census purposes). He could be one that is very specific on where he signs, so if you window bag your book and it is not where he wants, he could either ask you to remove it from the bag or remove it himself, both scenarios risk possible damage. Once the signature is completed the witness will then evidence bag and seal it. You will then need to return to the CGC booth to have them check it in for submission.
That is the 3 scenarios I can think of.