Heated O2 sensors are cheap and easy to wire up.
I would go this route and not worry about fooling with a toggle switch or
figuring out the correct voltage to send to the ECU.

So here's what I'm thinking. Rather than install a heated 02 sensor to
correct  the problem, why not just supply voltage to the ECU in the correct
amount to trick it into going into closed-loop mode? This could be done with
a transformer, a toggle switch, and a few long pieces of wire.

Start the van in open loop, drive for a few minutes, and instead of waiting
for the ECU to decide it's time, toggle it into closed-loop as soon as it
runs smoothly.

I say this because, having installed one of Ken Lewis' monitoring devices
for the O2 sensors, it's painfully obvious that I'm driving open-loop much
of the time, and thereby wasting gas.

Anybody done this? Heard of it being done? Any reasons it wouldn't work?