The only 'tricks' I can suggest are four methods:
1) Put dense, heavy items in your carry-on. I travel a lot, and am hardly ever weighed. Until my most recent Auckland -> London flight, when believe it or not, I had 10.5kg in my carry on, when the limit is 7, and Murphy's Law - they weighed it, first time I've had that in 10 years. We looked at each other, I acted awkward and surprised and pointed out my laptop was in there and was heavy, and my medication was in there too. She asked if I needed it for the flight, I said yes, she was relieved and waived it through :)
2) Duty-free bags. If you can get some, or get your carry on through - even if you're only allowed 1 bag (looks in RyanAir's direction) you're still usually permitted two duty free bags on even lost cost airlines (I use this example from Madrid to London, where there are signs pointing out this fact next to the duty free shops). Those won't get weighed.
3) Devious and you're stuffed if they check again - but you can get a friend to hold heavy stuff from your carry-on until you've had it weighed, and then put it back in. But if you're under supervision, this would surely raise all sorts of alarm bells!
4) If you're really desperate, despite all the weighing of bags and carry-on, most airlines don't weigh people - check to see if yours does (eg. Samoa Air does now). As such (and I've seen this done) you can wear as many layers as humanly possible, reducing your luggage - and of course, you can take most of them off on the plane ;)
Bonus fun fact: 11 years ago using carry-on and tourist bags from Hollywood, a friend and I took an entire stereo system, including speakers as carry on :D