You should be able to find exactly what octal value your CTRL+Z has by using od (octal dump), and then sticking that in your script.
See a good explanation on how to determine that here:
http://expect.sourceforge.net/FAQ.html#q54
Other than that, I have to say that Vidiyal's suggestion (trying with Q instead of CTRL+Z) has merit, and is a lot simpler.