The conventional wisdom says that your knee should be directly above or a little behind the pedal spindle. Of course, not everyone needs to adhere to that rule, but it's a good starting place. If you need more set back than your current seatpost and saddle allow, you'll need to get a seatpost with more offset (the degree to which the seat clamp is offset from perpendicular. You first need to figure out how much offset your current seatpost has and its diameter, and then go from there. Salsa offers some posts with a fair amount of offset. I've had good luck with AE Bike's selection, too (they're an online retailer).
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher