What's the problem with the centering mechanism? Well, helicopters require you to have a fine control over the aircraft. If you have to be continuously fighting the joystick that is stubbornly trying to get back to the center position, you will have to constantly be using your strength just to control the joystick, not the helicopter. There goes your fine control.
I used a rather old (but very trustworthy) Saitek X-45. The X-45 is an HOTAS system released back in 2001. One of the coolest features for us, helicopter pilots is the outside spring, that you can still see in the X-52, X-55 and X-56.
In the X-55 and X-56 you can replace or remove the spring which prevents the joystick from centering but also prevents you having to fight the stick the whole time. The older X-45 and X-52 don't have this feature, though. But this doesn't mean you can't still replicate it in an easy way.
All you need is a few plastic zip ties and some pliers or some sort of small wire cutter.
The idea is to reduce the spring strength or neutralize it at all. I prefer the spring to be completely neutralized so that I can control the joystick a little better.
Do to do, you'll need to compress the spring using your fingers or some tools. I use my fingers but if you decide to do so to, please beware: the spring is very strong and you can hurt yourself easily. It's not easy to pass the zip tie behind the spring and get it to exit so you will need to be putting a bit of strength and the spring can pop and hurt you. So, again, PLEASE, be careful.
The hardest zip tie is the first one. After you place it and tighten the zip tie, the other ones will be much easier to add.
You can probably get away with 2 zip ties. I use 4 just in case. After you place the 4 zip ties, you can cut them so that they don't get in the way.
After this your joystick will move freely, allowing you to control your helicopter with the tip of your fingers -- which seems to be how real pilots do too. Remember: helicopters are ladies that must be taken care of gently so be nice. As ladies they sure can make your live miserable if you don't!
I hope this small tutorial helps you achieve a better control of your joystick. Please use the comments section below if you have any questions, doubts or just to let me know if you tried it and what do you think of this modification.