Have you considered simply playing one class or the other with a multiclass? I realize that it's not quite the same thing, but having played around with this combination a bit myself I can assure you that you'll have difficulty keeping up with a group that's "fairly into optimizing" without some neat tricks yourself.

Based on what you've said, a sorcerer multiclassing rogue sounds like what you want. Pick up the feat from PHB2 to let you use ranged spells at melee through a dagger - Sorcerous Blade Channelling, I think it's called - and if you have access to dragon look into an article about 'The Shivs of Sorcery' for some more melee options. Sneak of Shadows nets you a 1/encounter sneak attack, of course, as well as Stealth to shore up your semi-rogue abilities. A background will net you another skill as a class skill (I advise Streetwise for a Changeling) and you're in business.