Long bar ends as drop-downs?

Yes - this is a known way to get stubby aerobars on a flatbar MTB, that don't stick out too far but provide some benefits of an aero position.

Downside is that you generally can't have brake levers, so your hands are a long way from the brakes. This is definitely not for urban riding of any sort.

Likewise, you're further from the gear shifters. Okay if you settle into a gear and stay there for a while, but not good in undulating roads.

Lastly remember that since your hands are closer together, there's less fine-control. So to start with it will feel very squirrely, and crosswinds can have a much larger effect before you can recover. Over-compensating is possible too.

Upshot: this is great if you have a long open road in your commute on a MTB, or if you have a gravel fire trail/track.

---

Normally these "Bar Mids" (instead of Bar Ends) would be attached to the bar inboard of your grips, brakes, and shifters. So all that has to come off the bars first.

If you do races on this bike, remember that many disallow the use of bar ends, so bar mids might be disallowed in the event.

They should work fairly well as aero bars or drops, so long as they clamp securely. On a good sturdy aluminium handlebar this shouldn't be a problem at the ends (drops) but as aero bars you may have to put them further apart than you'd like, depending on the taper of your bars. You will need to torque them up fairly hard, and test them in benign conditions. You may also wish to wrap them in bar tape (look for instructions for wrapping clip-on bars).

The lack of brakes will limit their usefulness, but most of us with clip-on aero bars don't have brakes on them. This means they're best for long (almost) flat sections with good visibility. It wouldn't be completely impossible to fit (cable) brake levers, subject to the diameter, but that would start getting expensive.

I have tried several bar end configurations, but particularly rotating them 180 degrees (downward) was not feasible for the next reasons:

1. The efective distance from saddle to hand position when on the drops is influenced by stem length and the front-going part of the curvature of the handlebar. That is, your hands touch a proper drop bar on a point further ahead than the handlebar clamp. Installing bar ends downward on a straight handlebar leaves your hands almost at the same distance than the handlebar clamp.

For reference, look at a side view of a real drop bar versus where the straight downward bar end would be.

2. The lower part of a drop bar is almost horizontal, thus your hands have a place to push down on. On a straight bar end you don't have that, the hand slips down and may even make handlebar tape slide off. Angling them backward solves this but places your hands behind the handlebar clamp and possible even behind the steerer clamp.

3. The dropped ends get too close to the knees so they are prone to hit you and also make it very weird to turn in tight radius.

In my experiment the handling resulted much too weird and unreliable, and would not result in a comfortable "aero" position: hands too close to body, elbows bent narrower than 90 degrees.

On another experiment I placed the bar ends between the shifters and stem. Either with short, straight bar ends and with long, inward-curved ones. Both resulted in, at least, one more hand position, which is good for long rides on smooth terrain.

The curved ones resulted a bit better because the curved part was rather long and provided a third hand position very far ahead of the regular straight handlebar. The riding position somewhat resembled the one on a TT handlebar, but lacked the arm rest, so I could not sustain it for too long. However, It allowed me to ride with my arms close together ( more aero?)

I wrapped these extensions with handlebar tape, installed them as close together as possible so they touched in the middle, so they form an almost contiguous arch.

Here is the most clear picture I preserve of the setup:

I definitely agree with Chris H's comment regarding this setup not being adequate for urban riding and I add that is not good for peloton riding either: hands are too far away from brake levers. It's only good for riding on open road with good visibility.

There is at least one commercially available product that should help overcome the issues mentioned above. (This is not a product reccomendation or endorsement of any kind, I have never tried these). However, you'd still have to solve the lack of brake levers.