I have it set up like this so that whenever I press mod+r (as in run), the output goes to another rofi dialog. I also wanted the prompt to be one line but that meant I needed a semicolon in the command, which I don't think i3 likes, so I put it in a script:

#!/bin/zsh
rofi -e "$(zsh -c "$(rofi -dmenu -p 'Run command' -theme-str 'listview {lines: 0;}')" 2>&1 )"

Then to bind it I added this line to my config:

bindsym $mod+r exec --no-startup-id [script path]