ThrottleStop works on anything Core 2 Duo or newer so yes, it will work on a Core i7-720QM.
The 1st Gen Core i processors do not support software CPU voltage control so you cannot use ThrottleStop or any software to change the voltage of these CPUs.
If your motherboard supports it, look for a 920XM on eBay. These Extreme CPUs have an unlocked multiplier and unlocked power limits. A 920XM can run twice as fast when fully loaded compared to the 720QM. Huge performance increase if you can find a way to keep it cool. ThrottleStop can be used to get the most out of an unlocked 920XM.