It's really dumb that QBO removed the ability to upload a scanned hard copy of a W9. Really the only reason you would even need the W9 in quickbooks is so you or your CPA can prepare 1099s. 

What I do is this:

1. Add them as a contractor and fill out all the personal details (IE - Business or Individual and put their EIN info in etc.)

2. Click on Vendors

3. Search for the name of the contractor

4. Click on it

5. Go to EDIT on the right

6. Make sure "Track payments for 1099 is selected"

7. In that same menu there is an option to "Upload Attachments". I just upload the hard copy of the W9 here and when it comes 1099 time, my CPA knows right where to look.