Digital Switch for Gas Fireplace
This answer assumes two things; first your #1 priority is a consistent look and second, it's important enough that you are willing to get creative. 

Thermopiles generate a small electric current using heat from the pilot light. This current powers an electromagnetic valve that controls the gas. It has been rightly stated that this low-voltage circuit cannot be controlled using the desired digital switch. The circuit requires a single-pole, single-throw mechanical switch. 

Here's my solution. Take your brand new Maestro switch and gut it. All you need is the visible exterior and the case that houses the digital goodies. Once the guts are removed, you will need to mount a latching push button switch in the case. This must be done in such a manner that pushing the touch plate will actuate the switch. 

I recommend securing the switch into position by filling the case with hot glue. Take a section of open-cell foam that is slightly thicker than the distance required to actuate the switch. Foam is often used for padding in packaging of electronics and optics and such. You have to be resourceful here, find some foam about 1/4" thick. The purpose of the foam is to hold the touch plate in position while allowing the plate to be pushed, actuating the switch. Cut a hole in the foam where the pushbutton will be, glue the foam to the case, then glue the touch plate to the foam. 

The finished product will look identical to your other digital switches while allowing operation of your fireplace without external power... all with a simple push on, push off function. Good luck Martin, I hope this helps.