Where to start...
First, to simplify your challenge, I would forget about the R-Thrust vs. E-Thrust issue, if you are like me it would only drive you nuts! As to converting R-Powered planes to E-Power, YES it can, and has been done. The first successful E-powered planes were either big gliders or scaled up R-Powered models. Something with a light airframe and lots of wing area.
Today you can convert just about anything, but the basic rules still apply... With enough power you can fly a brick... but it WILL fly like a BRICK. Stay away from heavy small models. You are starting at one of the extreme ends of viable RC so your choices will be limited. A light, RC assisted free flight model is (in my opinion) the best choice for the equipment and flying area you are talking about. Just don’t plan on flying it in any kind of wind.
Have you checked out:
http://www.skyhooks.ca/WES.htm
This is a great site with lots of "toys" in the class that you are talking about.
One other thought (although I don't know how good it is) is to pick up a $39 Wattage Micro Flyer. It comes with; a 150mah LiPo, transmitter with built in charger for the LiPo, receiver/esc, direct drive motor with prop and an actuator for the rudder. If you haven't flown RC, before I guarantee you will crash it if you try to fly it! But, if you were to strip out the gear and install it in a 1 to 2oz airframe with a larger wing I think it could meet your requirements. The main problem with this system is the limited range of the receiver. A good thing about this setup is that the rudder is normally in neutral, and the RX has to be receiving a signal for the motor to run. Translated, this means that when the plane gets out of signal range it just shuts down and goes into glide mode.
Humm... I picked up a WMF to keep in the car to fly during lunch but have found it to be less fun (flying it) than I expected... Your post has started me thinking about doing just such a conversion.