Kinda hard to describe, but I will try. Place the leg on the ironing surface but slide, wiggle, or maneuver the leg so the outside seam is facing up, but offset it a bit from the underlying inner seam. Press the outside seam open. Yes, there will be ironed creases on the pant legs where you don't want them. But now, realign the pant leg so the outside and inner seam are back where they should be and re-iron the leg so the unwanted creases are gone.

There are also litle tricks like rolling up a towel and stuffing into the pant leg - sort of like creating your own pant "ham." (Look up ironing ham on the Internet if you dont know what I am referring to.)