I agree with you on all the points except where you say it is not a duplicate. If the user posts an comment in the original postquestion asking for an text based offline solution there will probably be an answer there in the next day that will help him. If not he can create or ask to create a bounty that will attract 1 zillion answer to what ever is written on that bounty.
His question is a duplicate, only the best accepted solution posted on the original postfirst question will not fit him.
If you want to really help out ask him to post an comment on the original question, if you can, answer it with a nice guide, if you cant answer it, post his comment in the general chat from askubuntu. Someone will create a help guide for text based offline installs eventually and if fits for him will fit to many others thus making the original question more valid and the information all fitted "under one roof" instead of distributed.
Just because a question is centralized and an answer accepted as the most valid one does not render the original question useless for users that have only minor changes. In this case its only the GUI/text change, there are solutions for both, why not include them under the same question if that is a generalized one?
Plus there are already solutions on the original question that can actually help him, the USB mirror one will fit either GUI and text based systems. If you have another solution that you want to purpose you can add it to the original question and point the user to it.