Finally, a comm for that one user who hand-makes longbows. This ones for you, comrade.
If you've got access to a 3D printer, I would recommend this one: https://www.printables.com/model/300560-universal-u-lock-mount
It's what I use for my ulock. You'll have to measure the diameter of the tube on your bike, there's a few different variations.
I can make one for you if you want to hit me up on the DMs
I ended up printing one of these at my local library, it works like a charm! Thanks for the tip 
That looks to be exactly what I'd need but I don't have 3D printer lying around 
I also truly appreciate your offer but given the demographics of hexbear chances are you are in the US and sending something over to Europe would be too annoying and costly for you.
Do you have a friend, local library, or maker space that has one?
Seems a bunch of local libraries have 3D printers you can book for a tiny fee 
There's adjustable size / one size fits most U-Lock holsters out of fabric. Something like this, albeit you might wanna add some padding on the downtube in this example, an old inner tube or something. Also available for rear racks, easy enough to find, probably, on whatever local online shopping is available to you with the term "u-lock holster"
Alternatively if you're willing to tinker there's this idea, originally by /u/Bipro1ar on reddit who I do give credit because it's sick as fuck.
That one might involve some metalwork though, albeit I do think retrofitting a commercially available front rack with thicker PVC-pipes in this style of idea should be feasible with some gumption and a bunch of zipties.
I can't believe China's let me down with this. The only u-lock related products on AE I can find aside from actual locks are generic u-lock mounts which would be fine and dandy if the mounting bits on the lock hadn't snapped off.
These sorts of holsters seem to cost almost as much as I paid for the lock itself when delivered from online bicycle shops. They look like they'd do the job though
reusable cable binders? Dont know how much weight they can hold though
i put mine in the pannier
I dont know the shape of your bike frame but im guesing its triangle like. Here's my most simple idea: Tie two rope hoops on to the top bar of the triangle. To attach the u-lock:
Unlock the u-lock and thread it's bar through the two top loops so the lock is suspended from them. then lock it.
Using a short elastic cord with an easy secure mechanism. secure base of the u-lock to the bottom bar of the bike triangle, thus will stop it dangling
Ideally the elastic cord can remain attached to the bike when the lock is not attached
I wonder if cheap velcro straps like this could work? You can get a bunch of them for almost nothing but I'm not sure how tight you can pull them or how much weight they'll hold
There's some very specific and minimal ways of mounting ulocks depending on how your bike is setup. There are places you might be able to carry the ulock.
This product is just 3 big straps stitched together.
More DIY vibes.
I've looked at my bike from every angle and unfortunately there's no good places to stash the lock without it moving about or being in the way