Would not recommend
I have tried this - and it works well up to where it all went badly wrong.
So I had an old front wheel hollow axle with a QR skewer through it. There were two locknuts and two old cone nuts set at a distance of about 100mm, duplicating the OLD of a front wheel. Sorry no photos available.
This axle had been clamped onto a rear parcel rack as far aft as possible - since it was a test, there were jubilee/hose clamps and some packing. Effectively there was no movement on this part.
The towed bike had its front wheel removed, and the fork dropouts in the towing QR. The towed bike was angled upward like it was pulling a wheelie. I also strapped a couple of red blinky lights to the towed bike to make it more visible, despite this being a well lit summer evening.
I also fitted a secondary safety rope through the towed bike's frame and to my seat post. Car trailers must have them, seemed like a good idea.
The front wheel was strapped to the rear bike's chainstay and left pedal crank, the top tube and under the saddle to give three points of securing. Strapping was done with some reusable velcro cableties, which worked well.
Riding straight was fine. The towed bike was clattery and made a bit of extra noise. Reversing didn't work because I'd clamped down the pedal crank. That was not a problem.
Slow speed manoevers were okay - they felt really weird but turning at walking pace worked.
It all went wrong after about 10 mintes, when I was getting confident. I took a sharper turn at faster speed, perhaps 12-15 km/h when the back wheel lost all traction and I almost fell. I thought the towed bike had come loose or something.
On inspection everything was secured correctly. So what happened?
When leaning to turn, the third wheel (back wheel of towed bike) follows a shorter path than the front wheel and probably the middle wheel. But the QR was not able to rotate much, so that clamped on the towed fork, combined with the headset angle of the towed bike, lifted the rear wheel of the front bike. Unweighted it rose perhaps 2cm clear of the ground on a 15 degree lean. If the weight of the rider was there it would have risen less, but height doesn't matter once its clear of the ground.
The fix would be to either
build your towing mount so it has freedom to rotate in the same plane as the wheels (ie, the towed bike's back wheel can move up and down relative to the tow bike)
Set the tow mount lower, so that the effective angle of both head tubes is the same (or closer) Being ~10 degrees different was enough to cause this problem. You can't fit a front fork over a rear wheel because the OLD is different, but you might be able to suspend the tow fitment just aft of the front bike's rear wheel, or to somehow lash the towed fork dropout at the same place as the rear axle of the front bike but beside. The towed frame should clear the rear wheel, but keeping it straight might need extra thought.