I saw your auto-doser on hackaday, watched the video on youtube, read your thread here, and decided this was exactly the type of project i wanted to do next, so thanks for the awesome idea!!!
I went to Walmart and found the AirWick Freshmatic Ultra: http://www.airwick.us/access/html/pr...t_A000230.html
I also picked up a slim push pump soap, and probably the most exciting part of all, I found a Universal AC Adapter which has a voltage selector to emulate a wide range of batteries, from 3 - 12 volts DC / 600mA. I haven't had a chance to play with my supplies yet, but here is a picture of what the AC adapter looks like ... think it will work?
hope that helps!!