It's not that they bother me. As I said, I'll gladly help someone with a problem, and my record here proves that. But here's an example where you read about a method, and instead of trying it you're already coming up with hypothetical changes.

The conventional wisdom isn't always spot on, but it does have a good track record. A token effort at research would have found a number of methods along with supporting reasons and caveats, and this question would have been answered before it was asked.

BTW- since it isn't purely hypothetical -- the reason the spreader to simultaneously spread both sides won't work is that it's impossible to bend two pieces of steel at once. Steel has spring back properties and will only bend (or cold set) when it reaches yield strength, at which point, it relieves the load by moving. So as you add spreading force, one one side give, you cannot achieve the greater force to move the other. In the end all the movement will happen in whichever is the first side (usually, the right).

By analogy - imagine a strong man standing on a skateboard in the middle of the rope between two tug of war teams, and trying to pull both in. Once either team breaks down the other will pull him, and the fallen team to their side.