I stole this idea from "ridetoglide" on the Raleigh Twenty Forum. You flip a stock seatpost and stick it in the stock steerer, then use the stock stem tightener to cinch it down. It feels pretty damn secure and the extended height is great. You can either use a clamp-on stem for threadless systems or jam a regular threaded stem in the seatpost and tighten it up real good (i just tried that for mock-up and can't recommend it although it might be fine to do). I have no idea how this will hold up long term, but I plan to only use this bike on slow rides down the MUP. I posted pics of two different stems I had laying around.
DISCLAIMER!: I have not ridden the bike with this set up yet. I don't know if it's safe. It is just an idea. Please don't hurt yourself. Stay in school.