How can I emulate middle click in Windows on a touchpad?

Try this: Middle Click Simulator (direct download link)

Alternatively, have you tried installing he Synaptics Touchpad drivers?

I had a similar problem with a UX31 Zenbook from asus. They removed the ability to emulate a middle click. Once Elantech driver has been installed to replace the asus driver. Type "regedit" in the windows task bar.

Go to HKEY_CURRENT_USER/Software/Elantech/Smartpad Double click Tap_Three_Finger_ShowItem and enter the value 1 instead of 0. Double click Tap_Three_Finger and enter the value 2 instead of 0.

Then open "control panel" and "mouse" (in the small or large icone list)... In the tab ELAN under Options (one finger/Taper, you will find the three fingers option you are looking for)

Hope that it will help because it was a bit cumbersome for me...