Silly question: Did you try clicking cancel so it doesn't try to install DirectX?
I know, I know you probably don't even get that far before the crash. But I just thought I'd make sure.
Ash, maybe the installer could have check boxes that allow you to choose not to install DirectX and/or the VS libraries while making it abundantly clear that they are required for Construct to run. Maybe you would have to click on "Advanced" or "Custom Install" to even see these check boxes.