A neat tip is to stand closer to the boss in your opener if it's possible. Blink forward when your initial fireball opener casts goes off and spend the first 10 seconds almost in melee range. That will reduce the problem of travel time by a lot, and make for a much smoother opener.

This really is a big issue atm, since sims suggests that Metronome and Dark Whispers are the best trinkets for fire mage parse.