That’s my point. The problem is moved to a point further upstream - at the headwaters, actually - from which one of two downloads can occur and simplify the operator’s participation in a pre-determined process. I won’t try to dismiss your essentially correct assessment of the usual operators (including myself), but I really think that the download page, with the right visual design, can be made both attention getting and simple enough that practically any operator will make the selection appropriate to his/her needs. Getting the wording right for the two choices may take some finessing, but maybe you can put Bob on it. 
Having the choice on the download page has the added major (IMHO) advantage of presenting the operator right from the start with the knowledge that there are two different techniques available for installation depending on whether the target machine is connected to the internet or not. This forces him to think about it and the choice he makes sets his expectations and allows you to pre-configure the installation flow for the chosen method. It will eliminate, or at least reduce, the use of that famous utterance heard on cockpit voice recorders of automated aircraft around the world: “What’s it doing now???”