Do you mean the HDTV has NO HDMI Ports at all, or none left available?
If it has at least one HDMI port you can buy an HDMI Switch to share that port between devices.
*USB on TV's is usually a very limited video/picture functionality using the TV's media processing capabilities. It works with USB sticks and the interface is simple and the codec support limited.
I have a tv over 20 years old. It has only cable and component (yellow, red, white) connections. I was told by a Best Buy sale person to go on the Internet and get a HDMI to component converter. Plug the Roku into the HDMI port and the components into the TV. Make sure the converter is the type with power. It works great!