First of all, bear with me, I'm not a drummer, but I write drum lines for the music I compose on Guitar Pro. Now, its my understanding that you're typical closed hi-hat sound involves holding the cymbals closed with your left foot and hitting the cymbals with a drumstick. It is also possible to make pedal hi-hat sounds (just the pedal) and open hi-hat sounds (just drumstick).

I'm aware that devices such as drop clutches exist for freeing your foot for when using a double pedal bass. However, are there any devices that free your hand for this sound? maybe by stiffening the top cymbal so you can just use the pedal...

Guitars & Gear:
Parker Nitefly M
Sumer Metal Driver
Ibanez RGD2120Z
Two Notes Torpedo CAB
Well the pedal hihat sound isn't really anywhere near as loud as the closed stick sound. If you had an electronic kit though, I'm sure you could program it in.

"Show me war; show me pestilence; show me the blood-red hands of retribution..."
What are you trying to accomplish?
If it's just for time keeping, a pedal hi-hat still sounds good for that. Many drummers do that, and it sounds good.
If you want to be able to get the closed hi-hat sound at the same time as an open hi-hat sound, you can always get an x-hat mount with another hi-hat that is mounted slightly opened.
Things with strings:
Ibanez J.Custom, Prestiges, RG8, SR5 bass etc
LP's, Strat, Tele
ENGL Retro Tube 50
5150 III 50W
Orange Terror Bass