I like the comment about lockpicks and crowbars. It certainly feels like they’re using tools sometimes!
I’ve also had difficulty gluing things to plastic, and drilling isn’t always an option, due to the risk of thin plastic cracking. It’s bloody awkward, but using wire may be required. Tying a piece of a firm lure, like dried fruit, a firm piece of candy, or a piece of jerky, to the front of a T-Rex treadle might be a good thing to try, especially when they’re mounted vertically. Put in in the middle of the treadle, and then a loop from the lip of the hole above the bait cup to the front. In order to sink their teeth in, rats will have to put a decent amount of pressure on the treadle with their snout and/or paws. Because the lures are tough, mice, insects, and invertebrates will take a long time to eat it.
Jerky would be a good, hard-to-eat lure. In theory, it should be more effective at trapping brown rats, given their dietary preference for meat, but I’ve killed at least 50 ship rats using Goodnature’s Blood Lure (but it’s probably a much higher number) in my snap-traps, so firm, dried fruit, or candy may not be necessary (but rotating lures is a good technique). Goodnature’s lures aren’t eaten by ants here, which is a huge plus, and I’ve never found any evidence that larger insects or invertebrates eat it.
Dried fruit, like apricot, should be effective, and licorice All-Sorts cut in half, to reduce their weight and size to attach them to a treadle. If they eat All-Sorts, it should take insects quite a while to ruin them. There are quite a few gummy and hard candies that should work, instead of All-Sorts. A wide range of animals like anise, the substance in licorice that gives it its distinctive smell. Dried apricots should be more attractive to insects, but they’ll last a while, compared to soft lures like PB, Nutella, etc.
Regarding licorice as a lure, I knew a guy in Southland who used All-Sorts to trap possums, and he racked up impressive totals with it. This poses a problem in terms of possum interference, as do dried apricots, but they can both be used in Timms, and other possum traps with skewers, so placing a possum trap at the base of a trunk/post, or mounted vertically, below a rat trap, would be a good idea. Trapping expert Cam Speedy recommends placing traps targeting different species at the same site, in order to increase interaction-rates.
Once again, good luck! I hope the mini-treadle works.