My first couple brews I was really anal about cooling the priming solution to the same temp.
Then I realized, I'm racking 5 Gallons of 65 degree beer onto a cup or two of hot water. It will cool pretty quickly.
Since then, I cook the priming solution 1st, get everything else ready to bottle, and then just pour the solution in and go. I don't pay any attention to how hot or cold the solution is.
I haven't had any problems.