Below is a picture of an expansion plug. I purchased it from the local Ace Hardware store.
I installed it into the opening at the bottom of the steering column on the TRIcon. The idea is that if the handle bars work their way loose again, they will at least not fall totally off of the machine as they did before. I also have used a thread locking product to hold the bolts in place. You can see a bit on the bolt of the expansion plug.
Between this and stepped up diligence and maintenance on my part I won’t experience this problem again.
Thanks to all for all of your helpful suggestions and comments – much appreciated.