Don is right. Although there are methods and parts available to do what you are thinking, it's probably not worth the effort unless you happen to have all that stuff already laying in your parts box.
Kadee makes conversion couplers (20-series I think if I recall correctly) that have parts to switch your talgo truck to knuckle couplers. Among those parts are a couple different sizes of plastic adapter rings that fit on the pin, which in turn the coupler fits onto - eliminating the looseness or instability.
Sometimes it's a great fix, sometimes not - I've used them more for installing EZ-mates or McHenrys than Kadees.
But for a good, reliable uncomplicated fix that you won't have to tinker with again, use Don's advice
