Non-inverting amp with auto power on/off

Hi. I'm trying to create a non-inverting amp that turns itself on and off whether there's an input signal present or not. The idea is to have a low-power comparator with the input signal connected to the non-inverting input, when the input goes above a sertain threshold, it outputs HIGH thus turning on a mosfet. I've connected a cap from the gate to -V so that the mosfet will stay on for perhaps 5-10 seconds after the input is gone.

The problem is my virtual ground solution. It's created with a voltage divider with 4.7k resistors so this can't be connected all the time, the 4.7k resistor use too much power. The input's ground is connected to this virtual ground which means that the input is throught all the way up to +V when the mosfet is turned off, and then tossed back between +V and -V when the mosfet is turned on. I can't find a way for my comparator to make sense of this

Two possible solutions I've found is to use far higher resistors than 4.7k, but I'm afraid that is a bad idea. Another solution is to create a virtual ground with an op-amp, but then I would have to find a really low-power op-amp that can handle the current that the circuit demands. Does anyone else have a better solution. Here is a circuit to show the idea: