OK,
You can stuff a rod down it. That will transfer the bend and it will bend anyway.
You can fill the rod with epoxy. It will still bend.
You can add gussets. it will snap.
The stock post is cheap and soft. Sorry, that is just the way it is.
You can get a wildchild chromoly post (there are a couple other places that sell them, but his are the best). Problem solved. I was running a 6" riser with a set of aftermarket bars with a 2" rise built into them.
Been there done that.
I went the cheap route and ended up flat on my back watching my sled ripping across an area only to smack into a tree. The steering post snapped and when that happens you will pull on the bars and that will yank the throttle cable and put the sled WFO.
It cost me over 800 dollars in parts to learn.