Was going to propose some sort of mode or scale but being short on time and talent, I took an easy way out.

Play only in the open position.

Come up with a nasty, gritty song using only the open position. Play no higher than the 5th fret (some say open stops at 4th, but I found that too limiting). Use alternate tuning, whammy, tap, anything.

That’s it, develop a riff and then solo over it but go no higher than the 5th fret.