If they use a ratchet type of closing (like a hook/sheer that latches) there's a really good "drinks can" hack that you may be able to try similar to this How to make a Simple Lock Shim
Edit in response to Willeke's comment.
The basic process involves cutting and shaping a thin, sturdy, sheet of metal (a shim); which can be obtained "carefully" from cutting an aluminium drinks can, you can also buy shim from engineering suppliers/online; these are normally made of brass and may be too soft for some locks (the same with aluminium). If you find these metals are too soft, try some steel shim instead. Be aware, these metals aren't kind on ordinary scissors...
The premise is that you cut the shim to size, and then shape it accordingly so it can slide inside the opening between the bar that goes into where the locking mechanism is, and, the case that houses it. With enough force (care with sharp edges), the shim slides between the "bolt"/"sheer pin" (sometimes a ball-bearing), that is part of the lock internals, and between the movable bar that allows you to open and close the lock around things.
This is much harder to describe than picture :D
If this works with those cuffs... I've never "reverse engineered" them before...
There are also other items you can use to slide between the housing and the movable locking bar depending upon the type of lock you have. Being unable to see the type or style of lock that's in the Questioners' post, I am unable to determine the best route to take. However, ZipLock ties, (plasticuffs), and old style handcuffs can be bypassed in a similar fashion by sliding something between the "sheer" and the ratchet-shaped surface.
Some items include:
Sparkplug shims (they are quite handy as they come in many thicknesses, however they may be destroyed when using them for something like this)
Padlock Shims - often sold in packs of several sizes from locksmiths, these can be reshaped fairly easily with a file and some wet or dry sand-paper; they can also be repurposed for different lock types
Old-style metal sweet tins. However they can be quite thick; although these could be thinned using wet or dry sand-paper and some elbow-grease.
Other than that, I would recommend a "Junior Hacksaw". or a "mini-hacksaw" like this pictured: "Mini-Hacksaw"
(ok, apparently I need 10 rep to post more than two links!)
Thanks for the rep :) )
And! Hold the lock as sturdy as possible with an adjustable wrench, like this one, you want all that arm energy going into the cut, not moving everything about :P : "Adjustable Wrench"
Edit: I have been a hobby lock-picker for years. The time and effort involved in sourcing picks and trying to learn without breaking a lock, or breaking/damaging a cheap pick (I use Southord), you might as well just hacksaw it off considering hacksaws are cheap in comparison. Depends how much the cuffs were? but yes, time and effort, go for a hacksaw if it can't be shimmed...