If you use BA miles, you can have as many stopovers as you want on the direct route to the destination (on either of their partners that this would be useful domestically for: AA or AS).

Some award programs' rewards are mileage based, such as NH, and therefore allow you to use as many flights as you want under that limit. Depending on the total distance traveled, it could be worth it to you to look into that option (this would be on travel with any of their partners: US, UA, and CO).

Unfortunately, AFAIK all US-based mileage programs don't allow stopovers on domestic itineraries. Although, I do think that on CO you can spend an extra 10k miles to get a stopover.