In Autocad go into options, and then plotter setup. Follow the wizard to create a new plotter in autocad based on the HP Designjet, but as a destination select the IP for the plotter with a ‘problem’. See step by step images below starting from Options -> Plot & Publish
When in Autocad use the driver you created, when in windows use the system driver – simples!
C:\Users\%username%\AppData\Roaming\Autodesk\AutoCAD LT 2015\R20\enu\Plotters