I just finished building my bike and it doesn't exactly feel as if it fits me properly. My comfortable position is really with my ass hanging partially off the back of my seat. The frame size is 59 cm, and I definetely never had this problem on my last 57 cm frame. I took out two of three spacers to lower the bars but this only marginally effected my position in terms of reach. My seat is also all the way backward on the rails. So I guess my options are:

New seat with more sitting area

a stem with longer reach. Which might be nice since I hate the current stem

or a seatpost that flares backward?? Does the miche supertype do this?

My question is what would be the most practical way to solve this?

longer stem, I'd think. especially since you don't like the one you have, anyways.

flip your stem upside down. alot of people do that....one of the nice things about threadless set ups.
itll look better too.

yea, so you def want to fix that stem. get a stem with a drop and fix those bars too man, you have a very awkward angle created there. when your bars drop via the stem the bar ends should never be tilted above an imaginary horizontal line shooting out from the center of the bar ends. even horizontal is too much. you want them at a slight degrade so your arms naturally extend to the drops. (assuming you ride in the drops)
This should elongate your tuck putting you into a more natural position over your ride. If your finding that nothing is working then you may have not gotten a long enough TT on your bike my friend.