You know, I started to write a somewhat sarcastic answer to your question, because I thought it would be nigh impossible to manually add a print driver to a print server. So, I looked around to see how you would do it, and I have come to find it is not impossible. In fact, you can!
First, you need to modify a file called NTPRINT.INF
This file can be found in %windir%\INF directory on your print server. This is the file that lists all of the printer drivers by printer manufacturer. YOu would have to modify this file, putting in this printer in. Now, HP is listed in the [MANUFACTURER] section of the file, so you don't have to add anything in here. You would then go down to the MODEL SELECTIONS -> [HP] section.
Add your printer name in the left column, then in the right side, put a "= " and the print driver file. Odds are, the file will be a .PPD extension file. Just put in the file name with the extension.
Next, go down to the Installer Sections. Add your printer here, starting with the name of the PPD file the drivers use. Next, you need to set up a CopyFiles line and a DataSelection line. The whole mess will look similar to:
[driverfilename.PPD]
CopyFiles=@driverfilename.PPD,PSCRIPT
DataSelection=PSCRIPT_DATA
So, you need to find this PPD file. Also, it could be a .GPD file, or a .ICM. But most are PPD, from the looks of this INF file. Ok, save this INF file.