I’m afraid there is no elegant way to do this.
The layout “breakpoints” (to use web design nomenclature) are hard-coded and it would be nearly impossible to make them user-configurable.
The only solution I can think of (and you’re not going to like this) is to zoom out in your browser. Which would make everything very small, but would force the desktop layout.
If I think of anything else I’ll let you know, but that’s about all I have for you.